517eb1a1_Toppers___BedBathandBeyond_com__What_it_s_for
[Mattress Topper Type] Mattress Protector (a non-padded mattress covers) [What it's for] 
Non-padded mattress covers (sometimes called encasements) are designed to help protect a mattress from exposure to things that might damage it-like water, dust and dust mites, mold, pet dander, and other allergens. Non-padded mattress covers can be made of cotton, vinyl or super-tightly woven polyester fabric, and they usually zip up to totally surround the mattress. (You can get these encasements for box springs, too.)
Buying Guide to Mattress Pads & Toppers - BedBathandBeyond.com
What it's for