Depends on the item. I regularly mail postcard orders of up to 3 cards as non-machinable letters in #11 paper envelopes or in 6x9 paper envelopes. I line the envelope with thin cardboard (poster bard or file folder) and back each poly-sleeved postcard with the same. For 3 cards, the total weight is 2 oz. and the cost is $0.91 with the NM surcharge. Thickness is well under 1/4 inch. Bubble envelopes generally are thicker than 1/4 inch, even without contents, so they might be a flat (flexible) or a package -- but not a letter. First Class Package Service starts at 1 oz, although the current minimum online rate of $2.61 includes up to 4 oz. That is the least expensive cost for a domestic package. You can affix stamps to a package but the minimum retail rate is $3.00. Bottom line: You can mail small paper goods -- such as stamps, trade cards, postcards, stickers, photos -- as an ordinary letter if the result is not rigid or lumpy, is no more than 1/4 inch thick , weighs no more than 3.5 oz. and meets width and length limits. For example, a 2-page letter folded into a #10 envelope and enclosing a single 3-1/2 x 5 inch snapshot would be considered a letter. Additional rigidity would make it a non-machinable letter -- even some greeting cards are subject to the NM surcharge! ~~C~~
My Glass Duchess
Quoting Mom: In polite society, "hey" is for horses.