I use a needle-punched polyester batting for this type of thing. I like it for bags, wall hangings etc. as I like them to be a bit firmer than regular poly. The needle punching creates an almost felt-like appearance and the texture reminds me of those green pot scrubbers, lol.
Unfortunately I don't know who makes this as I order it on line from a small quilt company under the heading 'Firm needled poly wadding (batting)'. Someone might know who makes this in the US.