Skjoldehamn Blanket – this heavy, two-tone plaid blanket was part of a find that included an entire costume. Dated to the 11th century.

Wandering Elf reviews archaeological evidence (to help reenactors make correct costumes) and finds that Vikings tended to like plaids and stripes.

The examples strike me as not terribly different from the sort of tweeds used in British country suits.