These images, primarily from the Wenceslaus Bible of the late 14th century, were reproduced in Die Mode der Gotischen Frau by Olga Sronkova.
They supposedly depict members of the Guild of Bathhouse-Keepers in Bohemia, who may or may not have been ladies of easy virtue.
Their distinctive dress appears to consist of a spaghetti strapped or strapless, semi-fitted underdress, between knee- and ankle-length, worn with some sort of long flowing sash, possibly a towel. They carry badges of office in the form of a sponge/washing tool on a stick and a wooden bucket.
Two illustrations showing women in childbed also appear to show them wearing the same type of spaghetti-strap dress, suggesting that perhaps the bathhouse-keepers are actually simply stripped down to their skivvies for work in a wet environment, rather than wearing purpose-built clothing.
Comment: If you look carefully, it's pretty clear that the thing in his lap really is a backscrubber like all the other backscrubbers in the pictures.
Nonetheless, the outfits do seem to have become see-thru when wet:
Pictures of ladies in childbed: