Purchased in November 2016. Used only when my child visited, so the total usage period is probably less than a month. As it has been stored for a long time, I cannot guarantee its effectiveness in preventing dust mites. AllerSweeper Futon Cover Double Size 100% Cotton 145cm x 215cm I plan to compress it and ship it via Yu-Packet Post. This is a used item, so please understand the above before purchasing. Thank you.