Crawl Space Vapor Barrier Underlayment Felt550® is available in two sizes; 5' x 50' & 5' x 100' Felt550® was designed to protect the crawl space vapor barrier and other crawl space liners from punctures due to sharp rocks, concrete and metal in the crawl space. We highly recommend removing these items before encapsulating your crawl space, but that may not always be possible. Here’s an...