iMBAPrice 10x13 Inches White Poly Mailers - 100 Pack Waterproof Shipping Envelopes Bags for Ecommerce, Online Stores & Small Business Mailing | Perfect for Clothing, Jewelry & Lightweight Packages

They are indeed sturdy and waterproof, as determined by some fun testing I did: since they're so inexpensive (I paid $9.99 for 100), why not? First, I absolutely could not rip one with my hands. Then I cut one a little bit with a scissors (which the bag resisted); and then I could rip the bag a little more--which the bag resisted. Second, I put water inside and let it sit: no water escaped. Third, I stuck a weight inside another bag and immersed it in water: no water got inside. The only way water would penetrate is if it wiggled in through the seal, so, if I want to make something super-waterproof before mailing, I'll just give the seal an extra wrap with plastic sealing tape. Finally, writing. Photo: on the left is the initial results. On the right is what remained after I waited 2 minutes and smudged with a dry paper towel. Flair pen really didn't work (just little dots), and disappeared when smudged. Sharpie worked , although it almost disappeared when rubbed. Ballpoint (Uniball) pen worked and didn't smudge. However, my Avery labels were quite easy to peel off the bags. I never write addresses directly on any packaging or on a label without a moisture barrier because it's so easy to smear if the package gets wet, so I always use plastic sealing tape over my addressing for that purpose anyway. Plastic sealing tape stuck to the bags completely, unpeelable as long as no corner was sticking up. So I'm thrilled with the "bulletproof" quality of these bags. I especially appreciate that they're super-thin and take up absolutely minimal drawer space.