Update date: Aug 27, 2026 | 266 Pages | Report ID: M-AM-013618
Adsorption Heat Storage Zeolite Market
DMA IntelligenceWhat Is the Global Adsorption Heat Storage Zeolite Market Worth in 2026?
Segments: Product Type (Natural Zeolite, Synthetic Zeolite), Application (Residential Heating, Industrial Heating, Waste Heat Recovery, Solar Thermal Energy Storage, Others), End-User (Residential, Commercial, Industrial, Others), By Region, And Segment Forecasts
$1240.0M
Market Size, 2025
$1396.2M
Market Estimate, 2026
$3204.3M
Market Forecast, 2033
12.6%
CAGR, 2026–2033
Adsorption Heat Storage Zeolite Market Size, Share & Key Insights
The Adsorption Heat Storage Zeolite Market size was valued at USD 1.24 in 2025, and the market is projected to grow from USD 1.40 in 2026 to USD 3.20 by 2033, growing at a CAGR of 12.6%% during the forecast period 2026–2033. North America, Europe, APAC, Latin America, MEA led the global market in 2025.
Study Overview
 Study Period | 2021 - 2033 |
 Base Year | 2025 |
 Estimated Year | 2026 |
 Forecast Period | 2026-2033 |
 Historical Range | 2021-2025 |
| Units | USD Million |
 Coverage | Global | North America, Europe, Asia-Pacific, Latin America, Middle East & Africa |
 Deliverables | PDF + Excel Data Pack |
Major Market Players
Key Takeaways: Adsorption Heat Storage Zeolite Market
- In 2025, the global Adsorption Heat Storage Zeolite market size was estimated to be USD 1240.00 Million.
- Projected to grow at a 12.6% CAGR, reaching a valuation of USD 3204.09 Million by 2033.
- The Synthetic Zeolites category accounted for the highest market share of approximately 60% within the Product Type segment.
- Natural Zeolites captured a substantial 40% of the total revenue in 2025.
- Regionally, Asia Pacific emerged as the top market, generating USD 400.00 Million and securing a 32.26% share.
- Primary market growth drivers include increasing demand for renewable energy, stringent energy efficiency regulations, and advancements in material science.
- Key industry player Clariant AG strengthened its market position via continuous product innovation and strategic partnerships to expand application areas.
Market Definiton and Strategic Context
The Adsorption Heat Storage Zeolite Market refers to the global industry engaged in the production, distribution, and application of zeolite materials specifically designed for thermal energy storage through adsorption and desorption processes. These zeolites, known for their porous structure and high adsorption capacity, play a crucial role in enabling efficient and sustainable heat management across various sectors. The market encompasses both natural and synthetic zeolites, which are utilized in systems ranging from industrial waste heat recovery to solar thermal energy storage and building climate control. The primary objective is to store thermal energy for extended periods with minimal loss, contributing significantly to energy efficiency and decarbonization efforts. The market's expansion is driven by the increasing global demand for renewable energy solutions, the imperative to reduce greenhouse gas emissions, and the growing adoption of energy-efficient technologies in industrial and residential applications. The Adsorption Heat Storage Zeolite market size is influenced by technological advancements in material science, regulatory support for green building initiatives, and economic incentives for sustainable energy infrastructure. The market's growth outlook is robust, with continuous innovation in zeolite synthesis and system integration enhancing performance and cost-effectiveness. In 2025, the global Adsorption Heat Storage Zeolite market size was estimated to be USD 1240.00 Million, reflecting a solid foundation for future industry expansion. The market forecast indicates sustained upward trajectory, driven by the increasing integration of these advanced materials into mainstream energy solutions. The inherent properties of zeolites, such as non-toxicity, high energy density, and long-term stability, position them as key enablers for a more sustainable energy future, making this market a critical area for investment and technological development.
| Report Attribute | Details |
|---|---|
| Market size value in 2025 | USD 1,240.00 Million |
| Revenue forecast in 2033 | USD 3,204.27 Million |
| Growth rate | CAGR of 12.6% from 2025 to 2033 |
| Actual data | 2021 - 2024 |
| Forecast period | 2025 - 2033 |
| Quantitative units | Revenue in USD Million and CAGR from 2025 to 2033 |
| Report coverage | Revenue forecast, company share, competitive landscape, growth factors, and trends |
| Segments covered | Product Type, Application, End-User |
| Regional scope | North America; Europe; APAC; Latin America; MEA |
| Country scope | All; All; All; All; All |
| Key companies profiled | Clariant AG; BASF SE; Zeochem AG; KNT Group; Arkema Group; Honeywell International Inc.; Mitsubishi Chemical Corporation; Tosoh Corporation; Shanghai Hengye Chemical Industry Co., Ltd.; Sorbead India; Zeolyst International; Blue Pacific Minerals Ltd.; Interra Global Corporation; PQ Corporation; Grace Catalysts Technologies (W.R. Grace & Co.); Ningbo Jiahe New Materials Technology Co., Ltd.; Strem Chemicals, Inc.; Bear River Zeolite Company; Thermokon Sensortechnik GmbH; KMI Zeolite Inc. |
| Customization scope | Free report customization (equivalent to 8 analysts working days) with purchase. Addition or alteration to country, regional & segment scope. |
| Pricing and purchase options | Avail customized purchase options to meet your exact research needs. Explore purchase options |
Growth Catalysts & Market Constraints
The Adsorption Heat Storage Zeolite market is experiencing dynamic shifts influenced by a confluence of technological advancements, environmental regulations, and economic factors. The market size is poised for substantial growth, driven by the escalating global energy demand and the urgent need for sustainable energy solutions. Innovations in material science are continually enhancing the performance and efficiency of zeolites, broadening their application scope in various heat storage systems. This positive momentum is, however, balanced by certain constraints and challenges, such as high initial investment costs and the need for greater awareness about the technology's long-term benefits. Understanding these intertwined dynamics is crucial for stakeholders aiming to capitalize on the growth forecast and navigate the complexities of this evolving industry.
Growth Drivers
- Increasing global emphasis on renewable energy sources and energy efficiency is a primary driver, as adsorption heat storage zeolites offer a compelling solution for storing intermittent renewable energy like solar thermal and waste heat. This supports the transition away from fossil fuels, reducing carbon footprints and operational costs for industries and residential sectors, thereby boosting adoption rates in sustainable energy projects worldwide.
- Stringent environmental regulations and government incentives promoting green building initiatives and industrial decarbonization are significantly fueling market growth. Policies aimed at reducing energy consumption and emissions encourage the integration of advanced thermal storage solutions, positioning zeolites as a key technology for compliance and achieving sustainability goals across diverse applications, from HVAC to industrial processes.
Restraints
- The high initial capital investment required for implementing zeolite-based adsorption heat storage systems poses a significant restraint, especially for small and medium-sized enterprises. The cost of advanced zeolite materials and the complexity of system integration can deter potential adopters, leading to slower market penetration despite the long-term operational savings and environmental benefits.
- Limited awareness and understanding of adsorption heat storage technology among potential end-users and decision-makers act as a barrier to widespread adoption. The novelty and technical intricacies of these systems, compared to conventional heat storage methods, necessitate extensive educational efforts and demonstration projects to build confidence and overcome market skepticism.
Opportunities
- Expanding applications in the automotive sector, particularly for electric vehicles and hybrid vehicles, present a substantial opportunity for adsorption heat storage zeolites. Utilizing waste heat from engines or batteries for cabin heating and cooling can significantly improve energy efficiency and extend range, leading to new product development and market entry for zeolite manufacturers.
- Strategic collaborations and partnerships between zeolite manufacturers, system integrators, and end-users can unlock new market potential. These alliances can facilitate joint research and development, accelerate product innovation, and streamline the commercialization of novel zeolite-based heat storage solutions, thereby expanding market reach and fostering technological advancements.
Challenges
- The challenge of optimizing material properties for diverse operating conditions, such as varying temperatures and humidity levels, remains critical. Ensuring consistent performance and long-term stability of zeolites under different environmental stresses requires ongoing research and development, impacting product reliability and market acceptance if not adequately addressed.
- Standardization and certification issues for adsorption heat storage systems can impede market growth. The absence of universally recognized performance benchmarks and testing protocols makes it difficult for consumers to compare products and for manufacturers to ensure compliance, potentially slowing down adoption and hindering international trade.
Market Level Breakdown
The Adsorption Heat Storage Zeolite market is segmented by Product Type into Natural Zeolites and Synthetic Zeolites. Natural zeolites, while cost-effective, often have lower and less consistent performance compared to their synthetic counterparts. Synthetic zeolites, engineered for specific applications, offer superior thermal stability, higher adsorption capacity, and customizable pore structures, making them increasingly preferred for high-performance heat storage systems. This segment's contribution to the overall market is significant, as the choice between natural and synthetic zeolites directly impacts system efficiency and capital expenditure, driving innovation in material science to achieve optimal balance between cost and performance for various applications.
Segmentation by Application includes Industrial Heat Storage, Building HVAC Systems, Automotive, Solar Thermal Systems, and Others. Industrial heat storage represents a substantial portion due to the vast amounts of waste heat generated in manufacturing processes, where zeolites can efficiently recover and reuse energy. Building HVAC systems leverage zeolites for energy-efficient heating and cooling, reducing reliance on conventional methods. The automotive sector is exploring zeolite applications for engine waste heat recovery and cabin climate control, while solar thermal systems benefit from long-term heat storage capabilities. This diverse application landscape underscores the versatility and broad market potential of adsorption heat storage zeolite technology.
The End-User segmentation comprises Residential, Commercial, Industrial, and Automotive sectors. Residential end-users primarily adopt zeolite-based systems for domestic hot water and space heating, driven by energy efficiency and cost savings. Commercial buildings utilize these systems for large-scale HVAC and water heating, aiming for sustainability certifications and reduced operational costs. The industrial sector integrates zeolites for process heat recovery, which is critical for energy-intensive operations. The automotive segment, although emerging, presents a high-growth area for thermal management. This varied end-user base highlights the extensive reach of the Adsorption Heat Storage Zeolite market and its potential to impact energy consumption across multiple economic spheres.
Adsorption Heat Storage Zeolite Segmentation Breakdown
- Product Type
- Natural Zeolite
- Synthetic Zeolite
- Application
- Residential Heating
- Industrial Heating
- Waste Heat Recovery
- Solar Thermal Energy Storage
- Others
- End-User
- Residential
- Commercial
- Industrial
- Others
Geographic Performance & Regional Trends
Geographically, the Adsorption Heat Storage Zeolite market demonstrates distinct patterns, with Asia Pacific emerging as the largest market in 2025, driven by rapid industrialization, burgeoning energy demand, and government initiatives promoting sustainable technologies. The region's robust manufacturing sector and increasing investments in renewable energy infrastructure contribute significantly to its market dominance. Concurrently, Asia Pacific is also the fastest-growing market, propelled by countries like China and India that are aggressively adopting energy-efficient solutions and expanding their industrial capacities. North America and Europe also hold substantial market shares, characterized by advanced technological adoption and stringent environmental regulations, fostering the integration of zeolite-based heat storage systems. These regional trends underscore the global imperative for energy efficiency and the strategic importance of localized market development for sustained Adsorption Heat Storage Zeolite market growth.
Regional Growth Drivers
- North America: The region's strong focus on decarbonization and energy independence drives the adoption of advanced thermal storage solutions. Government policies and incentives, particularly in the United States and Canada, support renewable energy integration and industrial efficiency improvements, fostering a conducive environment for zeolite-based systems in commercial and industrial HVAC applications.
- Europe: Stringent EU climate targets and robust research and development funding for energy storage technologies are key drivers. Countries like Germany, the United Kingdom, and France are leading the charge in implementing adsorption heat storage zeolites in district heating networks and solar thermal applications, aiming to reduce fossil fuel dependency and enhance energy security.
- Asia Pacific: Rapid urbanization, industrial expansion, and increasing energy consumption in economies like China, Japan, and India fuel the demand for efficient heat storage. Government support for clean energy projects and the growing manufacturing base for zeolite production contribute to the region's position as both the largest and fastest-growing market for these technologies.
- Latin America: Modernization of industrial infrastructure and growing investments in sustainable energy projects, particularly in countries like Brazil and Mexico, are driving the adoption of adsorption heat storage zeolites. The region's abundant solar resources also create significant opportunities for integrating these materials into solar thermal energy systems for both residential and commercial uses.
- Middle East & Africa: Diversification of economies away from oil dependency and significant investments in renewable energy infrastructure are creating new avenues for market growth. Countries like Saudi Arabia and South Africa are exploring zeolite applications for industrial waste heat recovery and solar thermal cooling, aiming to enhance energy efficiency and promote sustainable development in the region.
Looking ahead, mature markets in North America and Europe are expected to continue their steady growth, driven by ongoing retrofitting projects and the integration of next-generation zeolite technologies into existing infrastructure. These regions will likely focus on optimizing system performance and expanding niche applications. In contrast, emerging markets in Asia Pacific, Latin America, and the Middle East & Africa are projected for more aggressive expansion, fueled by new installations, rapid industrial growth, and increasing awareness of energy efficiency benefits. Suppliers must tailor their strategies, offering customized solutions and localized support to address the unique regulatory landscapes and technological maturity levels across these diverse regional markets, ensuring sustained growth and market penetration.
Competitive Insights & Leading Companies
The Adsorption Heat Storage Zeolite competitive landscape is moderately consolidated, characterized by a mix of established chemical giants, specialized material manufacturers, and innovative startups. Key players often possess extensive R&D capabilities, focusing on enhancing zeolite properties such as adsorption capacity, thermal stability, and regeneration efficiency to gain a competitive edge. The market sees competition primarily on product innovation, with companies striving to develop zeolites tailored for specific applications like industrial waste heat recovery, building HVAC systems, or automotive thermal management. Strategic collaborations and partnerships are common, enabling companies to leverage complementary expertise in material science, system integration, and market access. Pricing strategies vary, influenced by material costs, manufacturing scale, and application-specific performance requirements. Distribution networks are critical, with major players utilizing global channels to reach diverse end-users across industrial, commercial, and residential sectors. Regulatory approvals and certifications, particularly for safety and environmental compliance, also play a significant role in market entry and expansion, particularly in regions with stringent energy efficiency standards. This dynamic environment necessitates continuous investment in technology and market development to maintain a strong position.
Leading companies in the Adsorption Heat Storage Zeolite market are actively pursuing various strategies to strengthen their market position and expand their global footprint. Mergers and acquisitions are observed as a means to acquire new technologies, expand product portfolios, or consolidate market share. For instance, a major chemical company might acquire a specialized zeolite producer to integrate advanced materials into its energy solutions offerings. Product launches are frequent, introducing new zeolite formulations with improved performance characteristics, such as enhanced cyclic stability or lower regeneration temperatures. Expansion into emerging markets, particularly in Asia Pacific, is a key focus, driven by the region's rapid industrialization and growing demand for sustainable energy solutions. Research and development investments are paramount, aimed at improving material synthesis, reducing production costs, and exploring novel applications. Differentiation is achieved through superior product performance, comprehensive technical support, and the ability to offer customized solutions that meet specific client needs. Companies also focus on building strong relationships with system integrators and end-users to ensure seamless adoption of their products. However, players face challenges such as margin pressure due to fluctuating raw material costs, the need for significant capital expenditure in manufacturing, and the continuous requirement for compliance with evolving environmental regulations, which necessitate agile operational strategies.
Adsorption Heat Storage Zeolite Key Companies
- Clariant AG
- BASF SE
- Zeochem AG
- KNT Group
- Arkema Group
- Honeywell International Inc.
- Mitsubishi Chemical Corporation
- Tosoh Corporation
- Shanghai Hengye Chemical Industry Co., Ltd.
- Sorbead India
- Zeolyst International
- Blue Pacific Minerals Ltd.
- Interra Global Corporation
- PQ Corporation
- Grace Catalysts Technologies (W.R. Grace & Co.)
- Ningbo Jiahe New Materials Technology Co., Ltd.
- Strem Chemicals, Inc.
- Bear River Zeolite Company
- Thermokon Sensortechnik GmbH
- KMI Zeolite Inc.
Adsorption Heat Storage Zeolite Market Ecosystem
Ecosystem Participants
- Raw Material Suppliers — Provide essential minerals such as aluminosilicates, silica, and alumina, which are fundamental precursors for the synthesis of both natural and synthetic zeolites. Their role is critical in ensuring the consistent quality and availability of basic components, directly impacting the cost-effectiveness and scalability of zeolite production for heat storage applications.
- These suppliers are often involved in mining and chemical processing, requiring adherence to environmental standards and efficient logistics to deliver materials to manufacturers globally. Their operational responsibilities include quality control and supply chain management to prevent disruptions.
- Zeolite Manufacturers — Specialize in producing various types of zeolites, tailoring their properties for optimal performance in adsorption heat storage systems. They focus on synthesizing materials with high adsorption capacity, thermal stability, and regeneration efficiency, which are crucial for effective thermal energy management across diverse applications.
- Their activities involve advanced chemical engineering, quality assurance, and continuous R&D to innovate new zeolite structures. They also collaborate with system integrators to ensure their products meet specific application requirements and performance metrics.
- System Integrators — Design, assemble, and install complete adsorption heat storage systems, incorporating zeolite materials with other components like heat exchangers, pumps, and control units. They bridge the gap between material science and practical application, ensuring the efficient and safe operation of these complex thermal management solutions for end-users.
- These integrators often provide custom engineering services, project management, and post-installation support. Their expertise is vital in optimizing system performance and integrating it seamlessly into existing infrastructure, addressing specific client needs and operational challenges.
- Research & Development Institutions — Consist of universities, national laboratories, and private research firms dedicated to advancing zeolite science and technology. They explore novel zeolite structures, improve synthesis methods, and develop new applications for adsorption heat storage, pushing the boundaries of what is possible in thermal energy management.
- Their contributions include fundamental scientific discoveries, patenting new materials, and collaborating with industry partners to commercialize innovations. They play a crucial role in validating performance, understanding material degradation, and ensuring the long-term viability of zeolite technologies.
- End-Users — Represent the diverse sectors that implement zeolite-based heat storage systems, including industrial (waste heat recovery), commercial (HVAC, hot water), residential (solar thermal, space heating), and automotive (thermal management). Their demand drives market innovation and adoption, influencing product development and market trends.
- End-users seek solutions that offer energy efficiency, cost savings, and environmental benefits. Their feedback on system performance and reliability is crucial for manufacturers and integrators to refine products and services, ensuring market relevance and customer satisfaction.
- Government & Regulatory Bodies — Establish policies, standards, and incentives that promote energy efficiency, renewable energy adoption, and decarbonization. They create the regulatory framework within which the Adsorption Heat Storage Zeolite market operates, influencing investment, technological development, and market growth through subsidies and mandates.
- Their role includes setting energy performance targets, providing grants for R&D in sustainable technologies, and ensuring environmental compliance. They also contribute to public awareness campaigns and educational initiatives, fostering broader acceptance and adoption of advanced heat storage solutions.
Report Coverage & Key Deliverables
The report delivers a comprehensive analysis of the Adsorption Heat Storage Zeolite, combining quantitative data with qualitative insights. It offers an in-depth exploration of market dynamics, segmentation, regional trends, and the competitive landscape, providing decision-makers with a holistic view of the industry. This meticulously researched document is designed to equip stakeholders with actionable intelligence necessary for strategic planning, investment decisions, and market entry strategies. By presenting both historical market performance and future growth projections, the report enables a thorough understanding of the industry's trajectory. It covers key market drivers, restraints, opportunities, and challenges, offering a balanced perspective on the factors influencing market evolution. The report's scope is global, encompassing major regions and countries, and provides detailed breakdowns by product type, application, and end-user segments. This structured approach ensures that readers can quickly identify critical trends and opportunities, making it an indispensable resource for businesses operating or looking to enter the Adsorption Heat Storage Zeolite market.
Report Coverage
- Market Size Estimates (historical and forecast)
- This section provides precise market valuation figures for the Adsorption Heat Storage Zeolite market, covering historical data from 2021 to 2025 and forecasting future trends up to 2033. The methodology involves a robust blend of primary and secondary research, including expert interviews and analysis of company reports, ensuring accuracy and reliability in market size estimations.
- Detailed Segmentation And Revenue Analysis
- The report offers an exhaustive breakdown of the market across key segments such as Product Type (Natural Zeolites, Synthetic Zeolites), Application (Industrial Heat Storage, Building HVAC Systems, Automotive, Solar Thermal Systems, Others), and End-User (Residential, Commercial, Industrial, Automotive). Each segment's revenue contribution and growth trajectory are thoroughly analyzed, providing insights into their market share and potential.
- Regional And Country-Level Insights
- A comprehensive analysis of the Adsorption Heat Storage Zeolite market's performance across major regions—North America, Europe, Asia Pacific, Latin America, and Middle East & Africa—is included. This section highlights regional market dynamics, growth drivers, and challenges, along with country-specific data to pinpoint lucrative investment opportunities and understand varying market maturities.
- Competitive Benchmarking Of Key Players
- This part of the report profiles leading companies in the Adsorption Heat Storage Zeolite market, offering a competitive analysis of their business strategies, product portfolios, and recent developments. It provides insights into market concentration, competitive intensity, and key strategies adopted by players to maintain and enhance their market position.
- Customization Options Based on Specific Requirements
- Clients can request customization of the report to align with their specific business needs. This includes options for deeper dives into particular segments, country-level analysis not explicitly covered, competitive profiling of additional companies, or detailed analysis of specific technological trends, ensuring maximum relevance and utility.
Recent Industry Insights
The Adsorption Heat Storage Zeolite industry trends reflect a period of significant innovation and strategic maneuvering over the past 12-18 months. Companies are increasingly investing in research and development to enhance the efficiency and durability of zeolite materials, focusing on applications that can significantly contribute to energy savings and carbon reduction. Partnerships between material scientists and system integrators have become more common, aiming to bring integrated, high-performance thermal storage solutions to market faster. Regulatory bodies globally are introducing more stringent energy efficiency standards, which in turn stimulates demand for advanced heat storage technologies. There's also a noticeable trend towards the development of modular and scalable zeolite-based systems, making them more adaptable for diverse industrial and commercial settings. Furthermore, funding rounds for startups specializing in sustainable thermal management solutions indicate growing investor confidence in this sector's long-term potential, driving further industry expansion.
Key Market Developments
- October 2024: Clariant AG announced a new partnership with a leading European HVAC manufacturer to integrate its advanced zeolite materials into next-generation energy-efficient heating and cooling systems.
- August 2024: Zeochem AG launched a new series of synthetic zeolites designed for enhanced thermal stability and adsorption capacity, targeting high-temperature industrial waste heat recovery applications.
- June 2024: BASF SE expanded its production capabilities for specialized adsorbent materials in Germany, signaling increased demand for sustainable thermal energy solutions across industrial sectors.
- April 2024: A consortium of Japanese research institutions and Mitsubishi Chemical Corporation unveiled a breakthrough in zeolite composite materials, promising higher energy storage density for solar thermal applications.
- February 2025: Honeywell International Inc. secured a major contract to supply its advanced zeolite solutions for a large-scale district heating project in Scandinavia, focusing on renewable energy integration.
- December 2024: Sorbead India announced plans to increase its manufacturing capacity in India to cater to the growing demand for adsorption heat storage zeolites in the rapidly expanding Asia Pacific market.
Analyst Opinion
The Adsorption Heat Storage Zeolite market outlook remains highly positive, driven by the undeniable global shift towards sustainable energy and increased emphasis on energy efficiency across all sectors. Analysts view the market as moderately consolidated, with key players continually innovating to deliver higher performance materials and integrated system solutions. Competitive intensity is expected to rise as more companies enter the arena, drawn by the significant growth potential. The demand-supply balance is currently favorable, with supply chains adapting to meet the escalating requirements from industrial, commercial, and residential applications. The market's attractiveness is further enhanced by the unique advantages zeolites offer, such as non-toxicity, high energy density, and long-term stability, positioning them as a critical component in future energy infrastructures. Investment in R&D remains a key differentiator, as advancements in material science directly translate into more efficient and cost-effective heat storage solutions, thereby expanding market penetration and adoption rates globally.
The long-term outlook for the Adsorption Heat Storage Zeolite market is robust, with significant growth anticipated due to persistent global energy challenges and the push for decarbonization. The innovation landscape is vibrant, characterized by ongoing research into novel zeolite frameworks, hybrid materials, and advanced system designs that promise even higher energy storage densities and faster charge/discharge cycles. Key risk factors include the high upfront investment costs associated with implementing these systems and the need for greater public and industrial awareness regarding their benefits. However, as economies of scale improve and technological advancements reduce costs, these barriers are expected to diminish. Strategic implications for suppliers involve focusing on scalable manufacturing, developing application-specific zeolite formulations, and forging strong partnerships with system integrators to offer comprehensive solutions. The market will also benefit from supportive government policies and increased funding for green technologies, further solidifying its role in the global energy transition.