PVC is lighter, completely moisture proof, and easy to clean. Melamine is heavy, only moisture proof on the surfaces, but is much easier to find for DIY'ers. It will swell if any moisture gets to the cut edges. Actually had one of my dogs pee on the bottom slot of one of my racks, which was empty, and the wood swelled so bad I couldn't get the tub back in. So, if i was buying new racks from someone else, I would get PVC over melamine any day. But I can't find a source for PVC, so I use melamine to build my own.