1. Priority Mail Padded Flat Rate envelopes are NOT available from your local post office or ebay, but you must go to USPS.com to order: (1) 15-count package of padded flat rate envelopes - I always order the maximum they will allow, which is 15. I set my google calendar to remind me regularly to order more as during holiday season I often use more than 15 in a week, and these take about 10 days to arrive or more, so order ahead of time. USPS requires you place a separate order if you want more than 15 padded envelopes.
2. Take the item you want to ship and lay it out and fold it carefully, pushing out all the air. I usually put it in a plastic shirt envelope (available from U-Line for about a penny a piece) and then I put it sideways inside a FREE priority mail TYVEK envelope, folding it in half and you can use the tyvek seal or seal with some priority mail stickers (also available only on-line- order a FREE roll of stickers)
3. Put the folded Priority Mail Tyvek envelope inside the padded flat rate envelope, along with a packing slip (for a top rated professional look - pretend you are a "real store" like Macy's who always includes packing slips!) Seal, and you are ready to go. Instead of a frumpy, bent up flat rate CARDBOARD envelope, you now have your item neatly packed in a padded envelope, making the customers feel like you are a top-rate professional store and care about your shipping and item.
4. Secure with packing tape on the outside. Depending on how much the item is protruding, I put packing tape wherever it might come apart. I always seal the "sealed close" part with packing tape as well, and put tape over the address in case of rain. NOTE: The padded flat rate envelopes are not quite as expandable as the flat rate cardboard envelopes. For example, one time I actually fit a men's W60x30 JEANS (not pants, jeans!) in a flat rate envelope and sealed it, which I cannot do in the padded envelope. I reinforced that pair of jeans with tons of tape, but it got to the international purchaser safely! For more information on how to pack any pair of jeans in a cardboard flat rate envelope, see my guide by that name.
5. Shipping cost: if you print through ebay, I believe it is $4.75 for a flat rate envelopes and $4.95 for a PADDED flat rate envelope. You'll have to decide if it is worth the cost.
I put some photos comparing the traditional flat rate envelope in size to the padded flat rate envelope - they appear similar but the padded doesn't expand quite as much, but it is more sturdy. If this helps, it you could take a second to rate this I'd so appreciate it! Happy Selling!