Are all mattress protectors waterproof?
Not all mattress protectors are waterproof, no. Some mattress protectors are instead designed to add a layer of comfort to the bed and to keep the mattress clean.
Most importantly, the ones that are waterproof will be labelled as waterproof or water resistant. You should be aware that water resistant means that some moisture may seep through, whereas water proof means that the moisture is prevented from moving down to the next layer, usually with the addition of a plastic layer in the middle of the protector.
The Interweave waterproof mattress protectors are made of a lightweight breathable polycotton with a waterproof layer inside to prevent water leaking through to the mattress. These mattress protectors have elasticated edges which wrap snugly around the corners of the mattress keeping the top and sides clean and dry.