[PaulK]

Did a quick research on plywood…
Plywood Strength

Mechanical Properties	Metric	English
Tensile Strength	27.6 – 34.5 MPa	4000 – 5000 psi
Modulus of Rupture	0.0483 – 0.0689 GPa	7.00 – 10.0 ksi
Flexural Modulus	8.20 – 10.3 GPa	1190 – 1490 ksi
Compressive Strength	31.0 – 41.4 MPa	4500 – 6000 psi

Though the thickness isn’t specified, It would seem to be substantially stronger than your foam.