The USPS template for "letter size mail" has a slot that is 1/4" wide. A bubble pack envelope empty will go through the slot. I have not been able to get a bubble emvelope with a chip in it to go through and be elgible for the 34c rate. Items that don't pass this test and are still under 1 ounce require an added 11c postage, making a total of 45c. That's what I use for most of my chip mailings.

You can get a free template for this purpose from your local post office. Ask for Letter-Size Mail Dimensional Standards Tamplate, D-1050251. It's good to have when you are shipping items in thin envelopes as there are other criteria that must be met to avoid the surcharge, such as the ratio between length and width of the envelope.