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.Worked as expectedMy wife and I end up selling a lot of stuff on ebay. Clothes we dont wear anymore, electronics, stuff we buy to resell...that said, maintaining packaging materials for all of that stuff becomes a nightmare. At one point our entire garage was filled with boxes we "planned" on reusing once we sold something of a similar size. It got to be too much. Noticing that some of the items we would BUY on ebay were coming in nice/tough bags like this, I invested in some myself.1. Most of the stuff we sell actually fits in these bags, so using a box is a more rare occurrence now.2. The bags are pretty tough. Try to tear through one, they arent like normal cheap plastic bags3. They are WAY lighter than a box for the equivalent storage size...which is money back in my pocket as I dont have to pay as much for shipping.All in all, great bags. Saved us on clutter, and we havent had one break on us yet.I use these to ship all my t-shirt orders on eBay They do the job perfectly, and have a cool color. They are thin to medium thickness bag. The adhesive is strong. Sometimes I do double up with these bags, but that's more about my OCD then the need to actually need to do that for protection. Within the past two weeks I've used just one for all my tee orders, and have had no complaints upon delivery. I have confidence that when I use these mailers my orders will never come open, and get there contents to the destination exactly as they looked when I sent them. I would recommend these for anyone who would need them for the same purpose. For XXL tees, I would recommend something slightly larger, unless you don't mind stuffing them into the bags, but I prefer a little extra room inside the bag just in case during the trip they don't pop from being too tightly packed. I use the next size up for XXL.These are the first bags I've purchased on Amazon for this purpose, so I don't have another brand/maker with which to compare. As long as they continue to do the job, I see no reason not to continue to use this product. I've had no issue with bags being stuck to one another, as some have. I haven't had to waste one of these to date.I need couple poly mailers so I purchase them and they are amazing & the perfect size. Not only that but the price is a steal for 100 poly mailers.I purchased these to package clothing for mailing and they're perfect for that purpose. They're large enough and heavy enough to mail a pair of jeans without any need for additional packaging, but lightweight enough not to add much weight to the parcel. The adhesive works well, I've mailed about 75 items using these mailers now and have had no issues with them. I'm about to purchase my second package, they make mailing so easy!They work great for shipping my product.I found these bags to be a great quality item for the price paid. They did not rip, tear or stretch like other similar priced brands that I have tried, not even when I sent a textbook. The black inner lining helps with privacy, which is a plus. The vibrant outer colors are sure to make the package stand out in the recipient's mail too!The selling point for me was the fact they use descent sticky sealant. That is the one place I usually expect the more cost-effective poly bags to cut corners on. But these guys made sure to build their self-sealing bags right. I didn't have to mummify my packages in extra tape to close them!There is no insulation protection to these polybags, so they are not recommended for jewelry or fragile items. But they are fantastic for books, stuffed toys, clothes, catalogs, and other more crush-resistant items. The fact it is naturally water resistant is a plus too.Strong sticking and materialOnly giving 4 stars! Some bags (approx 30) arrived ripped with the self sealing plastic coating off and they are useless to me. The rest were fine. Sturdy bags. Just a heads up outside the US you will be charged customs and duty on this product.good material, strong glue, tape sticks to it well. I'm happy with the purchase.Great value