Mike-
This is a common problem with light traps in 35mm camera backs. In one I
had repaired, the foam was replaced by some kind of fiber/felt material.
It hasn't been many years, so it is hard to tell how long it will last.
The adhesive will probably fail before the material.
For instrument cases, some kind of cloth covering the padding material
might be helpful. One candidate for padding would be from a pillow. I
had a foam pillow that lasted for many years without turning to gunk.
Fred
Depends on the type of foam. Black or dark grey foam has more oils in
it hence the reason why it turns into a greasy, gunky mess when it
passes it's cure date.( oils are an essential part of the pigment.)
This is also the reason why white foams don't turn to gunk. They'll
just turn yellow/brown and eventually flake to dust.
You could esaily replace the old black foam with white foam and it'll
work just as well. Just be sure to get the same density for shock
protection value.
You could also cover the white with fabric, either felt or crush
vallour/velvet.
Cut your white foam to fit the case as well as the instrument that'll
be stored in the case.(I use a long smooth edge bread knife sharpened
to razor sharpness. Utility knives and exacto's will work as well.
Just bear in mind that foam is a synthetic that really dulls any edge
quickly. have plenty of spare replacement blades on hand.)
Applying a cloth cover is easy. Just spray the foam surfaces with a
spray adhesive like Super 77(3M) and press the fabric as smoothly as
possible into the cutout for the instrument, the going in a circular
pattern outward press the remaining cloth onto the outer "top" portion
of the foam. Trim the edges leaving about an inch or two to spare to
allow for "tuck in" between the foam's edge and the case walls.
Another good foam to use is the type used in marine applications for
boat seating and padding. It's a hard, closed cell white foam with a
smooth finish. Good for high shock applications. Can be gotten at most
boat or marine supply shops. Also has the advantage of having a very
long cure date.(will last for many years.)
When used in conjunction with less denser foam in a multi-layer
configuration provides the greatest shock protection.( an inch or two
of marine foam on the case walls and two or so of soft foam on top)
Black foam is used primarily for it's cosmetic value. After all to
most guys black foam just looks cooler in a shock case.