We tried to test a number of strength characteristics including impact resistance (shown above), flexural strength, lap shear of glued joints, and nail holding. We discovered that our half inch wide samples were surprisingly strong, only the foam samples breaking or having their nails pull through when nearly 3000 grams of force was applied. Next time we'll use one quarter inch wide samples. Our glued joints, even with only one half inch of overlap, also held. However, few samples were able to withstand being struck by a swinging kilogram weight without snapping off!
The picture below shows the lap shear/nail hold set-up.
The picture below shows the lap shear/nail hold set-up.
We discovered that adding layers of thin paper or foil to both sides of weak materials like foam or plaster greatly improved their strength. Compare yellow foam to foiled yellow foam and foamcore, plaster to drywall, and balsa to plywood.