Gun case foam

I am sure someone here knows what kind of foam insert is best for gun cases.

I have had one insert basically disintegrate, stick to gun, etc., and another that contributed to rust as it maintained moisture. 
Also a couple of cases that are fine.

I looked online at Amazon and Ebay, and various inserts with differing chemical names appeared in search. 
Prefer soft semi-rigid that can be cut and shaped that does not retain moisture.

Local craft store had foam, but not sure if it was good for firearms.

Also, suggested places to purchase besides Amazon?

Thank you in advance. 
Kenn

I used a cheap bed foam mat from Walmart to line an old school hard sided leather briefcase . Kind of light tan foam. It has an egg crate side. It never gets wet but I keep a couple pieces of flannel cloths with oil on them to wipe off and wrap the pistols. This is short term most of the time. Not long term storage.

Most of these now are using a version of “Kaizen” foam.  Surf thru Amazon for sizes an options.  https://www.amazon.com/s/?ie=UTF8&keywords=kaizen+foam&tag=googhydr-20&index=aps&hvadid=409940679003&hvpos=&hvnetw=g&hvrand=1674633532779254564&hvpone=&hvptwo=&hvqmt=e&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9031348&hvtargid=kwd-44916267246&ref=pd_sl_7z248m9x53_e&hydadcr=24664_11410922

NYKenn wrote:I am sure someone here knows what kind of foam insert is best for gun cases.

I have had one insert basically disintegrate, stick to gun, etc., and another that contributed to rust as it maintained moisture. 
Also a couple of cases that are fine.

I looked online at Amazon and Ebay, and various inserts with differing chemical names appeared in search. 
Prefer soft semi-rigid that can be cut and shaped that does not retain moisture.

Local craft store had foam, but not sure if it was good for firearms.

Also, suggested places to purchase besides Amazon?

Thank you in advance. 
Kenn

I have done a lot of travel with multiple guns in cases. I learned the hard way to use closed cell foam specifically designed for instrument cases like the brand name closed cell foam listed above. 
The spongy stuff isn't nearly strong enough to support your valuable firearms during travel!

You probably had "ester" foam, it is soft open-cell and doesn't hold up well. It does work ok as a lid foam.

The codeword for semirigid closed cell foam is "PE" (polyethylene), which is what you want. You can buy several thicknesses and cut pockets at different levels so the grip, frame and barrel can all rest flat, it gets tricky with some guns. Bond them together with E6000 liquid qlue from a tube, which is a little fumey and takes 24 hours to cure, but it's stronger and way less messy than 3M 77 spray. The pre-cut Kaizen foams that Wobbley points to appear to be this material.

There are "high density" foams which are much finer-grained but they don't actually hold up as well IMO. You see this kind of foam used for optics retail packaging, I don't think they're a great choice for cases.

Don't store guns in cases no matter what kind of foam is there. Foam traps moisture and holds it right against the metal.

Other non-Amazon sources:
https://kaizeninserts.com/
https://www.carolinacustomfoam.com/
https://www.foambymail.com/

Thank you all for the comments.