Porphyran is a highly substituted agarose with a linear backbone consisting of 3 linked β-D-galactosyl units alternating with either 4-linked α-L-galactosyl 6-sulphate or 3-6-anhydro-α-L-galactosyl units. The composition includes 6-O-sulphated L-galactose, 6-O-methylated D-galactose, L-galactose, 3,6-anhydro-L-galactose, 6-O-methyl D-galactose and ester sulphate. Some of the ester is present as 1,4-linked L-galactose 6-sulphate. The precise composition of porphyran shows seasonal and environmental variations. Porphyran is not used commercially, but the seaweed, Porphyra umbilicalis is edible and is consumed in Wales (Laver). It is also made into a delicacy called Laverbread.