Troubles with closed-cell foam?

I have an old LL Bean bookbag/backpack which I intend to convert into a fair LF travel bag. Here's my scheme: I've gotten some closed-cell foam (chair padding) cheaply from the fabric store where my wife buys her sewing goods; the foam I have is 1" thickness. I intend to cut it to fit the front, back, bottom, and sides of the large main compartment, then contact-cement it into place. My Crown Graphic will fit easily into that compartment, along with room for other stuff (jacket, dark cloth, etc.), and the outer pockets will be fine for loupe, meter, film holders.
Here's the key question: has anyone ever had problems with this type of foam breaking down over time and leaving foam "crumbs" all over everything? If so, any suggested solutions? Thanks in advance.

There are many specific chemical formulations of foam. Personally, I have had some that disintegrate when touched by certain plastics, others that slowly decay and "crumble" , some have outgassed and caused my lenses to have a (removeable ) coating on them like a fog, and others that just seem to work OK.

You are taking a chance unless you know what you are buying, and more importanlty, what you should be buying. Buying from your local fabric store is probably one of the least probably places to get the right foam.

What I can not help with is the exact foam type or chemical description to help you. Others?

I have successfully purchased foam online from this source:

http://www.foamonline.com/

They have several types of foam which they list by density and longevity in years.

I've had a closed-cell backpacking sleeping pad for almost 15 years now that has yet to disintegrate. It's the blue foam found in backpacking stores everywhere and is the right thickness for padding and you can get large sheets of the stuff pretty cheap. Like this pad.

Go for a closed cell foam as Tom mentions, rather than an open cell foam (one where you can see the bubble holes) which will only last 4-8 years (for the beige coloured stuff) before you start getting bits of foam on your camera gear (beside the scraps left from cutting). The closed cell foam lasts for ages. My first camera pack was made similarly with open cell foam (cut with a hand jig saw), I used it for about five years... now 20 years latter it has disintergrated, and gets everywhere, but it did the job just fine at the time. I used contact cement to glue the backing on.

Now I use close cell foam (usually about 10 mm thick) though I am currently using 5 mm... I make sleaves for it out of ripstop nylon.. and have made quite a few good cases out of it... For the thinner closed cell foam try a yoga mat... Closed cell foam does come in different densities, I think the camera bag manufacturers use a very dense foam. There are shops that specialise in this stuff. (in OZ one is called Clark Rubber)

Just a tip on cutting foam. Aside from a hot wire, nothing cuts foam as well as an electric carving knife. It slices through without compressing the foam and makes clean professional cuts. The two blades going in opposite directions keep things from pressing and pulling. Use a guide of some sort to keep your cuts square. If you don't have one someone you know probably will. The going rate in the thrift store is $2.

Tom Westerbrook has the right type foam you want for your project. It can be purchased at any Walmart or sports shop. I have used it for years in biking and backpacking and now photography. It will outlast you no matter what you do with it. It is impervious to anything on the planet. And a razorknife will cut it just right. You can fasten it with a glue gun or contact cement. I used small rivets.