Rmax R-Matte Plus-3, 1/2 in. x 4 ft. x 8 ft. R-3.2 Polyisocyanurate Rigid Foam Insulation Board

Yes. R-Matte Plus-3 comes in 3/4" thickness. However, each Home Depot location carries specific thicknesses. The customer service desk may be able to order 3/4" if the quantity is sufficient. They may also carry Thermasheath-3 at 3/4". The current community answer provides a link to polystyrene product which is by NO MEANS an equivalent substitute for Polyiso.

I would think so , as 2 X 1/2 inches will make 1 inch ,it would be double. Great insulation, also GREAT SOUND BARIER.

Yes ... but you are making a mistake. A "dead" floor is a result of a solid floor. The "deadest" floor would be a concrete slab ... no vibrations or transmission of sonic energy. Putting 3/4" OSB on a concrete slab and making sure that there are no moving seams or gaps would give you the "deadest" surface. Now, to that, you are suggesting a layer of foam that can compress and then another layer of wood that can "thump" and vibrate. Can you do it? Sure. Will it work ... nope. And over time, it will get worse and worse.

No, vinyl plank flooring requires a rigid surface such as concrete or plywood. The insulation will crush under the weight of the floor and the traffic crossing it. Use plywood the raise the subfloor level. Mike

Eh.... This is rigid foil backed foam, and as such, won't dampen sound very well. You need something denser (regular weight drywall) or something absorbent (open cell foam- acoustic foam), properly installed roll fiberglass works reasonably well too.

It’s kind of a silver matte on the RMAX side and the reverse side is basically the same finish as aluminum foil so probably not ideal either. Assuming you have stud walls and not a pole barn type garage maybe consider unfaced batt insulation if you won’t be drywalling? Much more R-value

This may not be the best choice and it will certainly take some engineering knowhow to get it right, but it can work.

Good Morning, generally polyiso rigid foam insulation is of no harm to humans or animals when used as building insulation.

R-Matte Plus-3 generally needs to be covered with drywall products when installed on the interior of a wall surface. When used in an attic as a insulation box, it might be acceptable but the local code official would be able to verify.

It is not puncture proof. It will provide some padding and protection.