These mailing bags are low weight weatherproof very strong and 100 degradable they are 100 opaque so you can not see whats inside them and they also contain a tamper proof peal and seal flap once sealed they stay sealed and the only way to open the mailing bag is to tear it open mailing bags are a quick and hassle free way to send items through the post write on the bags using biromarker pen use address labels or document enclosed envelopes