Plastic with tracks to fit the cabinet. They have that bumpy top surface. And there’re white stains on all of them–toothpaste maybe? Have tried everything I can think of and no result. Really I’d rather just clean them.
Try Magic Eraser?
I’ve become a fan even though I thought they were a gimmick when they first came out. I’ve found them able to clean things regular cleaners can’t. They have a soft texture to fit around funny shapes and enough abrasive to get rid of stains.
Barkeeper’s Friend or Bon Ami is nice too. But always try the Magic Eraser first! They have a “bathroom” version which is larger, shaped differently and smells nicer than the regular one.