God, everyone, go the the P.O. page, print out the regs, take them with you, show the clerks. Quit argueing. It is clear right on their web site. A bubble envelope can be a flat. Never let them talk you into a parcel again. Ask them the flat rates, buy yhe stamps, take it home and put it in your mailbox. It only has to fail one of these three criteria to be a parcel. Nonrectangular in dimension, rigid or not uniformly thick. I can make any of my bubble envelope envelopes bend 1". If it falls within the dimensions and weight of a letter it is priced as a letter. I usually decide at home if the chip is going to go in a letter as one chip wrapped in paper and I send it from home. Even bubble envelopes from home. AVOID the hassle at the P.O. if you can. Weigh all mail and mail it from home. Most stuff I get comes without enough postage anyhow. Most of the time they never check. Just ask my favorite supplier. There goes my P. O. raise. :-)