How big? Wheres around here? Best source of PLY in denver IMO is Thompson Hobbies on wads just N of Colfax. This is the real mccoy--imported finnish Baltic Birch. It only comes in 5 ply lams I believe, for really good high ply count stuff have to do the internet I'm afraid.
J

I'd like to find at least a 2ft x 2ft section, but would prefer larger - like 2ft. x 4ft. I want to use it to make spars or linear ribs to strengthen thin walls.

I think that you should be able to design large rockets with the strength and structure originating in the core of the rocket, rather than with a thick walled exterior. All that fiberglass costs a lot and adds weight. Internal ribs and bulkheads should allow you to use a much thinner outer wall.

It goes to at least 18 x 36 inch, not sure re 2 x 4, if not they can get it. What thickness?

As to your comment about strength coming from the core, I agree in heart and typically build fins with thin g10 cores, balsa and CF covers. Gymnasts, acrobats, and dancers amaze me with their feats of strength with no apparent biceps, etc. Thats core strength. Little confused tho by the statement, you made re fiberglass adding weight and cost.

IMHO its dead wrong when it comes to rockets. The resistance to bending needs to be on the outside of the part, not the inside. Which I believe you know--as using any kind of built-up structure including stud houses, aircraft wings, what have you relies on this principle. 20 years from now very little will be built from metal in the traditional fashion--all fabricated from structural foam covered with laminates. This includes skyscrapers and bridges. Invest now in your favorite CF supplier!

Mick Kelly who makes composites for a living sent me some med density PU foam covered with CF. I keep a piece on my desk as a "paperweight" as it weighs less, but simply cannot be bent. You may as well try to bend a 3/8 inch slab of titantium. IIRC, has 4 layers of 6 oz CF on both sides.

I hit it with a 2 iron at 95 mph and left a barely perceptle ding. I've clamped one end in a vice and put a 50 # wt on the tip, zero or nearly so deflection. The stuff is amazing and I can see why bridges will be made of it.
JS