Postal Stationery "Soak Or Not"

We, or most of us, are familiar with soaking stamps, and the process of drying them in books to flatten them.

Has anyone ever tried to straighten a postal stationery item? I received a large pile of postal stationery items that are indicated as to have been involved in water damage. A few are stained, but the large portion are warped.

I don't think soaking them is a good idea, have thought about steam ironing, but was wondering if anyone out in SC land has attempted to deal with a problem like this.

Postal stationery & stamps are made of the same thing, paper, but NOT in the same way. Used items tend to run ink (it was water based ink way back when, before ball points came around) when put in water.
Then there is the glue that holds the envelopes together. That would certainly do damage if soaked.

I am not trying to make them more valuable, just trying to flatten them for display in my albums.

Any help, or experience in doing this, would be appreciated before I try letting my dogs sleep on the stuff for a couple of days!

I've never tried it myself, but would freezing while pressing between weights work?

Yes Puzzler Freezing and putting them in something flat will straighten them but just putting them in your album or whatever your keeping them in will eventually flatten them.

I wouldn't iron them. Yes, the steam wouldn't be good for the inks and envelope adhesives. But also heat is not good for paper. It's one of the causes of toning and it can weaken the paper's integrity.