At 01:19 PM 12/10/2012, Mike South wrote:
>Is the difference just that one is porous like a natural sponge and one is
>formed of a bunch of closed bubbles stuck together?  I saw a lot of
>recommendations that you use "open-cell foam", so I guess I'm wondering if
>that's the "default foam" :).

Open- and closed-cell foams are as you say.  If not specified you
don't really know which it is.  All else equal the closed-cell foam
will be harder to compress because you can't squeeze the air out of
it, but foam density, material etc. also influence how soft a foam
is.  It's been too long since I've been in a heater box (it's hanging
over my head, though) and I've forgotten what I learned while inside
them, but in general you don't have much force to operate the flaps,
so you have to have a light soft foam to be able to compress the
hinge side enough so the far edge seals.

Yrs,
d