Liquid Sun is a Finnish company based in Tampere that develops technology to convert captured carbon dioxide and water into synthetic aviation fuel (eSAF) using renewable electricity. Its low-temperature electrolyser system is designed to produce eSAF that can be used in existing aircraft without engine modifications, and the company describes its approach as a carbon recoding process.

The company was founded in 2022 to commercialise research from Tampere University and Stanford University, where Professor Mika Valden and his team developed a method for producing synthetic hydrocarbons. Liquid Sun raised a round of about €1 million in early 2023 and a seed round of nearly €4 million in November 2024, led by Voima Ventures with Failup Ventures and Business Finland. The funding supports Finland's first pre-commercial eSAF demonstration plant, housed in a 66-square-metre container.

Liquid Sun started up a CO2 valorisation unit supplied by GIG Karasek (now GKT) in 2024 and signed a cooperation agreement with Vataset for raw material production at the Kemijärvi Biopark. In 2025 it launched an eSAF pilot in Espoo with ABB, Finnair, Fortum and Finavia, with Finnair and Finavia providing local offtake partnerships. Soletair Power has also partnered with the company to use captured CO2 for eSAF production.

The company was selected for the IAG accelerator programme in 2025 and was named among Europe's 10 most promising climate tech startups by EU-Startups. Its target market is the aviation sector, where EU blending mandates are expected to create demand for synthetic fuels.