I wasn't sure which forum to put this under, but here goes. I've used the acid free hard foam board for displays before, but would 100% polyester like the replacement pads sold for lawn furniture be safe? I'm looking for something to use for a case to display several small knives in. Something like the cases that squeeze the knives between the glass and foam, but I want to make sure my padding won't damage my blades or handles. I know the polyurethane foam is a no-no, but thought the polyester might be safe.

don't think so,,polyester has some kind of outgassing. Turns color with age,,I wouldn't chance it... There's got to be sort of acid free / everything free batting sold somewhere.
We used to have a great topic on places that sold all kinds of supplies like that.. Slim chance but maybe try a Search...

Sometimes I forget my daughter is a lic. professionally trained conservator!!

She said do a search on:

'Hollinger Metal Edge' - That they will absolutely have what you want. and they ship everywhere.

Thanks for the link! I found they actually sell polyester batting as well as a number of other polyester materials. So perhaps it depends upon the type of polyester. The cushion material I was looking at is 100% polyester and they claim it won't discolor with age. But I'd sure hate to find out the hard way that it wouldn't work. I do have some polyethylene thin foam that I've used for years for storing handguns in. I'd forgot about that until I saw it on their website, but it doesn't offer quite the compression I think I'd need. I may cut up a few sheets and give it a test run.

my daughter tells me that IF you don't see exactly what you want give them a call and sometimes they can help you out!

Thanks. I appreciate the assistance!