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This vintage men’s bathing suit is from the 1920s or early 1930s. No makers label, just a content label saying that it is part wool.  Feels like the rest is probably cotton, because, if anything, it feels like a soft cotton knit T-shirt.  It has a skirt and side cutouts. Sizing on these one pieces can be a bit tricky- please refer to the measurements. 
Waist unstretched: 13″ (doubled = 26″)
Waist stretched: 20″ (doubled = 40″ )
Shoulder to crotch unstretched: 22″   
Shoulder to crotch stretched: 26″