Pristine® is one of the best know allergen barrier fabrics on the market. It is a patented, membrane-free, micro-weave polyester fabric that feels nice to the touch. It has a small, 5.7 micron pore size that provides great protection against dust mites and their allergens. Pristine® dust mite covers are cool, quiet and breathable to sleep on and are unnoticeable under your sheets. A huge benefit of the Pristine® fabric is it can withstand frequent laundering and still retain its tight weave and small pore size. One more thing to note, the larger size mattress covers will have a seam in them as the fabric is only made 66 inches wide. This will not bother most people because the covers are covered by your sheets, but is worth noting for those who are picky about seams.