stuart noble wrote in news:XRdgr.32840
:


Try Rockwool. Ridiculously cheap at B&Q. You may need to prevent the
insulation becoming compressed by the soil.

Thanks; your suggestion gave me another idea: polyurethane foam, as used in
Celotex wall board, etc. I seem to recall that it absorbs water like a
sponge, but doesn't compress significantly.

Al