Blue hydrogen is produced by the process of

Blue hydrogen is made by steam reforming of natural gas or methane, paired with carbon capture.

Electrolysis powered by renewable electricity instead yields green hydrogen.

Steam reforming of bituminous coal produces hydrogen classed by a different feedstock.

Steam reforming of lignite is likewise not the defining route for blue hydrogen.

The colour label reflects the feedstock and whether the carbon emissions are captured.

Grey hydrogen uses the same reforming but without capturing the released carbon dioxide.