Polyethylene
From BelegarthWiki
Polyethylene foam is a strong, resilient Closed-cell foam. Polyethylene can be more durable than Blue Camp Pads and can be substituted for Camp Pads in any Belegarth weapons construction context, and is the foam used in all Edhellen sword blades and punch shields. However, polyethylene foam can vary wildly in quality and durability. While it can be found relatively inexpensively at Foam By Mail, that foam has repeatedly been found to be useless for weapon construction due to its poor durability. It can reportedly still be used effectively for punch shields, however.
Evalite, often considered the best known closed-cell foam is actually a particular formulation of polyethylene foam - "cross-linked, EVA-modified polyethylene". Volara is another polyethylene foam used in weapons.
