Not for me. I used 1/4" acrylic sheet. You can probably get thicker. Also depends on how it's supported and what you're keeping in there. I think 1/4" in a mini fridge for sodas, snacks, a lunch bag would be fine.

I had the same issue and got some 1/4" thick acrylic sheets at the home improvement store. Cut them with a sawzall or fine tooth hack saw or jigsaw. Masking tape over the line you cut to prevent it from chipping or cracking.