This is not a waterproof sheet. I was using it to temporarily lay my baby down. It's recommended not to use it for long periods or in a baby bed, as it can come up. It's about the size of a baby bed. I don't think there's any overall yellowing or discoloration! I've set the condition to "slightly scratched and dirty." I'm just a regular person, so I don't think there are any noticeable spots, but I think there are some minor signs of use, flattening of the padding, and small stains. Please refrain from purchasing if you are sensitive to these details.