Frank wrote:

I'm trying to apply some expanding foam to the inside of a
closed garbage bag that's situated between two surfaces that
are about an inch apart.

I'm discovering that the small amount of foam that's leaking
out of the fill-holes is expanding and curing nicely, but the
foam inside the bag seems to be semi-solid goop. I'm leaving
this over night to see if it's any better tommorrow

The canned foam needs water to make it set. It gets this from the
air. So, in an enclosed space it won't go off unless you spray
the surfaces inside with water.

Decent article on chemistry:

http://en.wikipedia.org/wiki/Polyurethane

Bubbles in the foam are from carbon dioxide liberated when
isocyanate reacts with water. In a two parter water could
be in the polyol

So this morning the foam inside the bag was still a mix of ridgid or
cured/expanded parts and a lot of goo-ee parts. So I poured a couple of
cups of warm water in from the top, which saturated everything in the
bag for a short time before leaking out the bottom through some holes I
didn't know were there.

No detectable change in the goo factor.

So I take everything apart and put it on a horizontal surface and open
up the bag. Some expansion and curing did happen naturally, but the
water treatment had no effect. Most of what was there was skinned over,
encapsulating large pockets of goo.

When I broke the skin, it seemed to just stayed in a goo phase or state,
with no tendency to immediately start to expand and harden. Maybe this
will eventually happen if I leave it exposed to air for another few
days, but something has certainly changed the pace at which the goo
expands and hardens.

So there must be some time factor involved beyond just making sure this
stuff is exposed to ambient, humidified air.

and two parter is needed by op.

Too expensive, and too hard to source locally.