I don't know about the particular foam I imagine it is a form of expanded polysterene but don't know for sure.
Is your concern for rock detail or for light weight? What is the rock wall for particular species or a general cage theme?
Each answer has its own particular type of rock wall and the best way to make said wall.
The varieties go from carved expanded polysterene pieces to mesh and concrete each has its advantages and disadvantages.
Let us know, size can also be a factor.
Good Luck
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Jeremy
"I am become death, the destroyer of worlds" July 16, 1945 Robert Oppenheimer
1.1 Double Het "Sharp" Snow RTB's
1.1 Hypomelenistic RTB's
0.2 Pastel Hypo RTB's
2.0 Double Het Stripe Albino RTB's
0.1 Suriname RTB
0.1 Anerthrystic RTB
0.0.11 Red Bearded Dragons
1.1 Rhinoceros Iguana's
1.0 Green Iguana
1.0 Ball Python
1.1 Cream Golden Retrieviers
1.0 Pomeriaian
0.2 Catus Terribilis
0.1 Spouse
0.0.1 Youth -coming soon-