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For individual investors
Carbon13
SEIS Fund X
Early-stage investment in the UK's most promising climatetech ventures for the 2026/27 tax year.
Closing end of October 2026
Get in touch
Request the information memorandum and our investment team will be in touch.
High-risk investment. You may lose all your capital. Tax reliefs subject to individual circumstances. Risk summary.
Fund X at a glance
Reasons to invest
Why Carbon13 SEIS Fund X
Our approach
We build ventures.
We don't just pick them.
Carbon13 builds and backs ventures addressing climate change. Over four years we've supported more than 1,500 founders and helped build over 300 climatetech startups from day zero across the UK and Europe.
50% of ventures are hardware-based, tackling some of the hardest problems in climate: energy, AI, the built environment, advanced materials, transport, carbon removal and food systems.
To learn more about how we build ventures, request information above or register for one of our investor community events.
Portfolio highlights
Three ventures built to scale
Founded from day zero on a Carbon13 Venture Builder programme, and now backed by leading climatetech investors.
Low-carbon cement
Cocoon
Cocoon transforms the by-product of electric steelmaking into LoopCem™, a scalable, low-carbon Supplementary Cementitious Material (SCM). They aim to become the largest SCM supplier in the US and Europe in the next 10 years.
Carbon13 were vital to the genesis of Cocoon, as the Venture Builder is where our cofounding team formed, and where we built the core proposition for the business, both commercially and in terms of its carbon impact.
Eliot Brooks, CEO & Co-founder, Cocoon
AI materials discovery
MatNex
MatNex uses AI software to transform the way new materials are discovered and designed. Using rapid automated processes and advanced quantum calculations, they work with partners to reduce global CO₂e emissions and accelerate the discovery of next-gen materials from decades to months.
We were part of the first cohort in Carbon13, and it was an amazing experience that has shaped our company today.
Jonathan Bean, CEO, MatNex
Carbon & natural capital insurance
Kita
Kita is the carbon and natural capital insurance specialist. Through their insurance products and risk advisory services, they help companies participate confidently in the growing market for carbon and natural capital assets, while upholding the rigorous risk management standards expected by stakeholders.
One of the hardest parts about starting a company is finding somebody to do it with, and Carbon13 brought together a pool of incredibly intelligent and motivated people, all focussed on climate change and all ready to start a business.
Natalia Dorfman, CEO, Kita
To read more about their rounds and valuations, request information above.
Important: Portfolio companies are shown for illustration and are not an indication of the holdings of Fund X. The value of investments can fall as well as rise. You may get back less than you invest. Past performance is not a reliable guide to future results.
The team
Who's behind the fund
Tax relief benefits
What SEIS means for you
Tax treatment depends on individual circumstances and may be subject to change.
The Seed Enterprise Investment Scheme, or "SEIS", is the UK Government's scheme to incentivise investment into UK startups through tax reliefs. In the tax year 2024–2025, £272 million was invested through this scheme.
Follow-on investors in Carbon13 portfolio companies
Get in touch
Interested in
SEIS Fund X?
Complete the form and our investment team will be in touch.
High-risk investment. You may lose all your capital. Tax reliefs subject to individual circumstances. Risk summary.