As fabric always cotton. As a pattern colored on the warp yarn along the weft, this usually manifests as small square checkerboard rather than a stripe (vichy).
Why would I know? Fabric is a near universal trade good (normally stores value a little better than food) and the adoption of mass production economies based on technical innovation and fashion (own a Beaver Hat?) quite historically significant.
Only acculturated values of Puritan, Victorian, and 50s gender stereotypes make my expertise the least bit remarkable.
It is still a pattern favored by mods (Paisley? You were watching U.S. TV during all the important parts of the 60s).