Neoprene wetsuit bibs. Men's Large listed size, but they seemed to fit more like a medium. I measured them at 4/32" thick, or ~3mm. They are old, but I never wore them more than a dozen times. They have a front zipper and zippers on the calves, and they all work.
I'd keep them but my waist isn't 30" any more, and they'd better fit someone who is about that size and is under 6' tall.