That may sound like a stupid question but...
For reasons beyond this topic, I wanted to make the cardboard tube from
the inside of a paper towel roll a bit more rigid. Ahah, thought I,
fill it with expanding foam.
Just so it didn't spill out all over the shop, I shoved a Sainsburys
carrier (I'm sure other supermarkets are available) in the middle and
squirted said foam into that, so the tube acted as a former.
Result: Only the foam at the open end expanded and set properly.
Just in case it was the carrier bag, I lined it again with some thin
plastic sheeting and repeated with the same outcome (except that after
leaving it overnight, the unexpanded fraction had set).
Squirted a bit onto a piece of cardboard and it swelled up etc as normal
(so it's not a duff can).
It's not low expansion foam or anything, just bog standard Screwfix stuff.
So, what is it lacking that it gets normally - oxygen, nitrogen, water
vapour? Or is it that it doesn't like the plastic? I never seem to have
a problem getting it to expand when I squirt it into quite deep holes in
brickwork etc. (ie it it always makes more than I want/need/expect)
I know this isn't the most important question ever asked, but I'm