What Adhesive Is The USPS Using On Modern Self-Adhesive Stamps?

Hi all – What adhesive is the USPS using on modern stamps? I've seen it described as "pressure-sensitive adhesive" (PSA), but I don't know what that means. Is PSA supposed to be different, more pressure-sensitive, than any other adhesive? It seems like all adhesives would be "pressure sensitive", so I'm confused by the label.

Moreover, what is it? I mean chemically. Do you think it would be good for making envelopes? I seems like it bonds to paper very well, so I thought I might use it on envelopes. (For the bottom, pre-sealed flaps, and the final closing flap.)

When I look at adhesives used in the past, I see gum arabic, dextrin, and PVA. I can make the gum arabic at home from powder, and I've also seen a gelatin and sugar formula for homemade envelopes. That would be easy to make as well. I'm not sure if I can make dextrin or PVA.

I was confused to learn that PVA is Elmer's glue. I thought Elmer's was supposed to be a joke, not serious glue, more like edible goo. Apparently PVA is a decent adhesive, and is used in a lot more contexts than just Elmer's. It's part of the Mod Podge formula, which a lot of people seem to like. All this time I thought Elmer's was a wheat paste or something...

The modern stamps seem to adhere nicely, without any goop or wetness. It would be neat to have that efficient adhesive for envelopes. Do you think the envelope manufacturers are using the same PSA that the USPS uses for stamps? If I can't make it, where can I buy it?

Thanks.

My local Staples store sells several kinds/sizes of envelope with a removable backing strip which reveals the self-adhesive on the flap ready to seal.

Also, the USPS doesn't make stamps. To generalize very broadly, since the 1890s, the Bureau of Engraving and Printing (BEP) produced the great majority of their stamps. Now the great majority are contracted out to private companies. I suspect the formulations are proprietary, but which meet the performance requirements of the contract.

"pressure-sensitive adhesive" (PSA) also known as self-adhesive is entirely different than the gum arabic, dextrin, and PVA which are water activated, while PSA is already sticky. As far as I know you can't just buy a jar of PSA (and even if you could it would be hatd to spread), but as JB has already noted tey already make envelopes with PSA on the back flaps.

If you would like to kill some time reading about PSA's:

https://www.sciencedirect.com/topic...ive-adhesive

Oh thanks for the link.

John, I thought the USPS brought production in-house, after a period where they used outside firms, which was in turn after the BEP arrangement ended.

I figured this ain't rocket science, so there wouldn't be a lot of pomp, proprietary, secret, etc. static on it. It's just sticky wicky. If someone's envelope or stamp adhesive was better than everyone else's, I'm not sure anyone would notice. Well, maybe if it was a huge improvement.

USPS has no in house production capabilities

Creating a modern stamp is quite scientific. And most modern US stamps that are pressure sensitive are essentially non-soakable.

They're non-soakable? I thought they fixed that after their aborted introduction of self-adhesive stamps in the 1970s... How do people get them off? I just got a bag of used stamps in the mail, and some are probably self-adhesive.