I recently bought some thin clear plastic molds. These are not silicone and cannot bend without breaking or cracking up. I tried making some of the designs this weekend and even though I was able to get the fondant in, I was unable to get the finished piece out in any usable form. I tried putting cornstarch in the mould, putting crisco and putting it in the freezer. Nothing worked. Can someone please help. I really need those design pieces for a cake I am working on.

Wash the moulds and make sure they are dry - and start again.
Sometimes using CF/CS can make the cold fondant a bit gluey - iykwim.

I would use a little dab of bakers joy / non stick spray
Put the fondant in
Pop in the fridge or freezer for 5 - 7 minutes - not only will this make it set up faster - but the fondant shall shrink just a fraction.
Give the mould a good quick tap on the bench to loosen the fondant that way it should just pop out.

Works for me - hope it works for you.

Bluehue

Bluehue.

Just a thought try putting one layer of saran wrap in the mold & press the fondant into it, I do that with my cutters, not sure if it'll work but worth trying
HTH

Thanks for the tips. Will let you know how it works out.