Using ordinary materials from a hobby store, I'm going to demonstrate what makes a structural insulated panel (SIP) so strong.
This thin sheet represents an OSB (Oriented Strand Board) skin, similar to what you would typically find in a SIP. It’s only about an eighth of an inch thick, whereas real SIP skins are usually much thicker—typically 7/16 inch, 5/8 inch, or even three-quarters of an inch.
The rigid foam insulation I'm using here is about three-quarters of an inch thick. In actual SIP construction, the foam cores are much thicker—ranging from three and a half inches up to eleven and a quarter inches, depending on the application.
Here’s the second skin layer.
When we set these three separate pieces—a skin, foam core, and another skin—loosely on a span and apply a 10-pound dumbbell to the center, followed by another 10-pound dumbbell, you can see how much the structure bends under the weight. There’s significant deflection because the pieces aren't connected.
Now, using the exact same materials, we glue or laminate the three pieces together to mimic the bonded construction of a true SIP. When we apply the same amount of weight to this laminated structure under the same span conditions, you can immediately see how rigid it becomes. There's minimal deflection, showing how much stronger the panel is once the layers are bonded.