Italian to English Other Textiles / Clothing / Fashion bedding/linens and things

I can't find anything that fits this meaning. Here the term traversa is used to indicate a waterproof protective swath stretched over the center of the mattress to protect it. It is not a mattress cover because it does not cover the entire mattress. It is not a mattress pad because it is not padded. But I haven't the slightest idea what I could call it. I have seen them in hospitals but this is to protect the mattress for home use.
Any ideas