The undetectable layer of polyurethane makes these mattress protectors 100% waterproof without the awful feeling of lying on, or being sandwiched between, a crisp packet! Gone are the sweaty, rustling plastic sheets that so many people dread and in their place is an ultra soft, breathable mattress protector made from pure brushed cotton. Importantly, the discreet, undetectable layer of polyurethane that makes the mattress protectors waterproof also acts as an anti-allergy barrier. It protects against dust mites, a major cause of two increasingly common conditions ? asthma and hayfever.