If nothing but letters can be sent in an envelope then why do they offer it as "Rigid, non-machinable" for a surcharge? Obviously they can make whatever rules they like but the problem has been getting everyone to understand just what is allowed and what isn't. I ship one or two chips in a plain envelope with the cardboard protectors around them. I ship them out of my house also which avoids all of the cage critters arguing just how much the postage should be. And Cindy giving the letter carrier a nice Christmas present last year probably did not hurt. When I ship more chips I use an bubble envelope and make sure that there is only one layer of chips (to avoid problems with the "less than 1/4 variation" requirement) and ship it as a non-machinable large envelope. I wish they would get rid of all of the requirements and just use weight to determine shipping cost.