Dried seaweed sheets
Thin, toasted sheets of pressed red seaweed, crisp, with a salty taste of the sea.
Plain sheets for sushi are sold in many supermarkets in the Asian aisle, while the seasoned kind common in Korea, toasted with sesame oil and salt, is mostly found in Asian grocery stores. Plain sheets can be seasoned at home: brush them thinly with sesame oil, salt them lightly and toast them briefly in a dry pan.
Substitute:
There is no real substitute, because both the flavour and the crisp sheet come from this seaweed. For seasoning, crumbled nori flakes from a shaker come closest in taste, though not in form.