We've been using StockPKG while poly mailers since the first week they were offered for sale, and I can't say enough good things about them. They weigh almost nothing, so the postage savings compared to the corrugated shipping boxes we were using more than paid for these mailers. The price of these mailers is very low, but the quality is very high. There is no way the self adhesive strip can be pried open once it's sealed, making these mailers extremely tamper proof. The thin and flexible polymer material is cross linked so it's incredibly tough and puncture resistant. Mostly, I love the fact that these poly mailers require very little storage space and they're clean, without the cardboard dust from boxes, and both of these features have cleaned up our shipping department. The only issue we've had is when trying to mail a very small item in a flexible poly bag, we had a few that didn't reach their destination because they disappeared in the US postal system. It's possible that the thin envelopes with almost nothing in them to give them shape don't play well with mail sorting equipment, but I see that as a problem with the USPS and not with these poly mailers. We put small items in bubble mailers that have a stiffness of their own. This is the largest of the three sizes of StockPKG poly mailers we use.