How do the pros make or buy panels like this?

Consider Corian (a dupont brand) for countertops. It is heat and scratch resistant but lighter than granite. Cost about the same. Laminate might be too thin.

 

Yes. I have as also seen some stone veneer they make now you can bend just a bit. Real granite. Apparently very light due to how thin.

 

Strange follow up question.

If I wanted to make a table or some small item like a cabinet face, couldn't I just use 6lb Airex T92.100 and laminate a plastic laminate bit on it without using any fiberglass at all??

Seems like for things that take no load (not steps of course) this could make a pretty stiff and nice looking panel.

Anyone see anything wrong with this?

 

That seems do-able to me. In fact, what you describe is pretty close to SIP, Structurally Insulated Panel, used in buildings, walk in coolers etc. It might depend on how big the panel is, but if it was say a cabinet face, a shelf connected to the backside would help reinforce by cutting down the unsupported panel size. It might not even need reinforcing.
When doing cored fiberglass or panels like you propose, where hardware is attached or screws or bolts are concerned, you would insert some wood or plywood for the screws to dig into or to give crush strength for bolts etc.

This is how lightweight hollow core doors are made for houses, with a perimeter frame of wood, a block for where the doorknob and latch are and usually the core is cardboard on edge. Doorskins are about 1/8 inch thick plywood. You can buy doorskins by themselves sometimes but they are usually limited to an odd size like 37 x 82, just a little bigger than the usual largest door. They are very nice plywood creations though as they are thin, made of 3 plys and they have a light fiberglass scrim imbedded inside which makes them pretty tough. They are excellent for re-usable pattern shapes. They come in different woods also, mahogany for sure.

I have a panel I experimented with years ago, maybe 2' x 2' with a 3/4 x 3/4 wood perimeter, a piece of styrofoam filling in and formica contact glued on both sides. The edges are rounded over a little bit and the wood left exposed and varnished. I never used it but it's tough enough for any cabinet doors.
I think you could do 4x8' panels for walls or whatever size you need using wood perimeters and the blue or pink styrofoam from home depot and contact cement. The edges could be left exposed as above or squared up and formica'd as the open door is in your top photo.

 

What an amazing thread. A heartfelt thank you for your responses. I've learned so much from this thread I think I'm ready to give it all a try.