[Boatanchors] Packing Material

[Keith Densmore]

Greetings Fellow Anchorites,
Having not shipped a heavy item for several years, I went to the local DIY
shop for a couple of sheets of the  rigid white foam insulation sheets I
always used for the inner packaging. I was dismayed that they no longer
carry the stuff.
A quick search on the internet suggests all retailers are in the same
situation.
Question. Assuming stiff foam boards are not available, what is the
alternative? Material must be rigid to support heavy items,  light weight,
and be relatively thick. Thanks for the help.
Keith ve3gem