What material can be used to minimize cubic feet?

[supermaxx123 10+ year member]

that expanding foam, would overdo it maybe

 

[iamamp3pimp 5,000+ posts]

is this a sealed enclosure?

 

[ngsm13 5,000+ posts]

Clay.

nG

 

[Gs04Aero 10+ year member]

is this a sealed enclosure?

yes sealed enclosure

that expanding foam, would overdo it maybe

I was going to go with thick foam cut to fit into the opening and secure it. It's no much space but its enough to change my cuft value.