D-mat is a company for our sustainable future, which employs experts in various fields. We aim to advance one planet lifestyles; a resource-wise and low-carbon life. D-mat is specialised in carbon and material footprint calculations as well as researching and mainstreaming sustainable lifestyles. Our services are suitable for companies, government agencies, research institutions and social enterprises, among others.



+358 40 541 2876 (FI)
+49 15 15040 2619 (DE)


Michael Lettenmeier

Research, consultancy, speeches

Michael (Doctor of Arts, M.Sc., Environmental Science and Policy) is the chief executive officer of D-mat ltd and one of the leading experts of resource efficiency and dematerialisation in Finland. His consultancy, training and research activities in Germany and Finland cover sustainable consumption and production, measuring and monitoring carbon and material footprints, eco-efficiency, ecological rucksack and MIPS, and the sustainability of companies, households, municipalities and transport systems. Michael has conducted and supervised sustainability assessments and footprint calculations for numerous companies, supervised dozens of master’s theses, and produced and edited a large variety of publications in the field of sustainability and eco-efficiency.




Viivi Toivio

Carbon and material footprints, consultancy

Viivi focuses on developing procedures and tools for the carbon and material footprint calculation of households and lifestyles, as well as for individual products and services. She is also consulting and training households, municipalities and companies in their transition towards one planet thinking. Viivi has developed several lifestyle carbon footprint tests and contributed to the development of the Climate Puzzle as well. She holds a Master's degree in Environmental Ecology, and also works as a consultant for D-mat at the Hot or Cool Institute.

Viivi is currently on maternity leave, during which inquiries regarding her areas of expertise can be directed to Jari Kolehmainen.




Jari Kolehmainen

Carbon footprint calculations, research

Jari's responsibilities include carbon footprint calculation, developing data models and data tools along with other data analysis. He is a Master of Social Sciences and a qualified software developer, whose multidisciplinary studies included environmental policy, atmospheric physics as well as data science. Previously, Jari has worked at the Finnish Environment Institute (SYKE) and at the Centre for Consumer Society Research at the University of Helsinki, where he conducted household intervention research that aimed to reduce energy consumption.




Salla Lahtinen

Project management, Climate Puzzle, workshops and accelerators

Salla's responsibilities include the coordination and implementation of various projects, especially the Climate Puzzle, the 1.5 degree lifestyles workshops and the sustainable lifestyles accelerators. During the workshops Salla operates as a facilitator as well. Salla studies at Aalto University in the multidisciplinary Creative Sustainability Master's programme and has a background in fine arts.

During 1.1.–31.5.2021 Salla is on study leave, during which she is substituted by Daniel Leiviskä.

D-mat ympyrä



Oona Korpi

Human resource management, Climate Puzzle

Oona's duties include in particular the day-to-day management of human resources and tasks related to the employment lifecycle. Among else, she is responsible for Climate Puzzle customer relations and invoicing as well. Oona is currently finalising her Bachelor of Business Administration studies at Haaga-Helia University of Applied Sciences, in the Multilingual Management Assistants degree programme. In her studies, she has specialised in leadership and human resources management.

Annastina Saari D-mat



Annastina Saari

Consulting, research, communications and marketing

Annastina's main focus is in carbon footprint calculations, marketing and website developmentIn addition, she helps organize accelerators and workshops. Annastina has a MSc degree in Economics and Business Administration from Aalto University and is currently studying in the Master's programme in Forest Sciences at the University of Helsinki. In her studies, Annastina has concentrated on information and service management, UX design and international business. In her Master’s thesis, she analysed the UX of SUSLA carbon footprint calculator and its effects on user behavior.

D-mat ympyrä



Ursula Rinta-Jouppi

Carbon footprint calculations, research, consulting

Ursula is working with carbon footprint calculations, calculators and data analysis especially with Jari. Ursula is also involved in helping to organise workshops and accelerators. Previously she has worked on projects such as My Carbon Action and the translation of the Climate Puzzle into Swedish. Ursula is studying Environmental and Food Economics at the University of Helsinki, with a minor in Mathematics and Computational Methods. In addition to her work at D-mat, Ursula also works as a teacher.




Sonja Nielsen

Research, Climate Puzzle

Sonja’s expertise lies in combining service design methods with sustainability science, especially related to climate change mitigation and the circular economy. She has developed the educational design game the Climate Puzzle, which is used to promote 1.5 degree lifestyles in educational and municipal contexts in Finland and abroad. Sonja holds a Master’s degree in Creative Sustainability from Aalto University. Previously she has worked as an environmental consultant and service designer in several consultancies, as well as a communications lead for citizen movements.




Sanna-Liisa “Sannis” Sihto-Nissilä

Research, carbon footprint calculations

Sanna-Liisa is responsible for the further development of D-mat ltd's footprint calculation tools. She holds a PhD degree in atmospheric physics and a Master of Science degree in engineering, and has broad experience in climate change related research and education. In her PhD thesis, Sanna-Liisa studied the climate effects of aerosols. In addition to her work at D-mat, she teaches climate change courses at Aalto University and participates in the higher education institutions' national Climate University project.

Sini Kolehmainen



Sini Kolehmainen

Climate Puzzle, content for communications

Sini has among else worked on the Climate Puzzle and footprint calculators. Sini holds a Bachelor's degree in Theology. Her background is philosophical and ethical, and environmental issues are close to her heart.


In addition, to get more deeply acquainted on the current topic or commission at hand, D-mat ltd employs other experts of relevant fields, consultants, educators and interns.