USPS has new regulations for 1st Class Mail envelopes with 1/4" thickness restrictions. A 6x9" envelope which is the size that patterns fit in can go for 1st Class postage, but, if it is more than 1/4" thick, it has to go for the "large envelope" rate which is $.80 for 1st oz. instead of the $.44. They have a heavy cardborad measuring devise that if your envelope does not "fall" throught the slot, it does not meet the thickness requirement.