Foam Core PVC
- Foam core is allowed for DWV applications, but not in pressure applications
- Not as strong as solid core - more deflection - . But that actually makes it last longer, according to wikihow?  and this  explicitly stating it's longer-lived than solid core.
- Stack Exchange says it can bend more , some jurisdictions don't allow it but only in commercial construction.
- There is a significant difference for direct burial. Only 1/2" gravel or smaller is allowed for foam core. .
- Foam core is ASTM F891  while ASTM D1785 is for solid core (pressure pipe)