The fabric looks like broomsticked cotton. To get those crinkles, you take a damp length of fabric, twist it tightly, and let it dry twisted. Broomstick skirts were popular in the 1990s.

My, isn't she feeling superior!

Of what material are their costumes made?
Looks like a seersucker effect. Did the Romans have seersucker togas?

This is Diana and nine of the nymphs who hunted with her. See, for example, the story of Callisto in the second book of Ovid's _Metamorphoses_ and the story of Actaeon in the third book. Callisto, one of her companions, was raped by Zeus and then expelled from the troupe by Diana when it became obvious that Callisto was pregnant. When the hunter Actaeon accidentally saw Diana and her companions bathing, Diana turned Actaeon into a stag, and he was torn to pieces by his own dogs. I believe that the woman seated in front is meant to be Diana.

Rather attractive group of girls considering that their clothing seems to be made of flour sacks and burlap bags.