I host swaps and the manilla envelopes do not hold up very well.. Ive had more problems with that than all the rest. They look like they went thru he!! and back.. Most are torn, and Ive lost the entire contents of one so far sent to me- And no the contents were never found. I do not recommended them for my swaps, however i do request that if any of my swappers choose to send in those envelopes please use packing tape and 't' the envelope with the tape, Make sure contents are in a plastic baggie marked with mailing addy- To and from.