plastic.  yes.  very snug.  these shoes don't run exactly small, just snug.
i like the adjustable strap.  hard to get on your foot if wet.  or been sweating and take them off.
i take my shoes off to drive and put them back on.  tight.
i can't wear plastic shoes and i must have had a weak moment when buying these.
thought i'd like them.
the rolling heel was comfortable.  i hope someone at goodwill finds them and enjoys them !