Plywood is made up of multiple layers of wood that have been combined with various chemicals such as PHENOL FORMALDEHYDE and UREA FORMALDEHYDE.
To make waterproof plywood, ply must be made with phenol formaldehyde to protect the ply when it comes into contact with water or moisture.
The number of major plywood failures is due to water and moisture only.
And SHIGMA PLYWOOD is such a plywood that anyone can boil it in a pressure cooker for more than 15 whistles.

As a result of this experience, anyone can tell how strong the waterproofing is on the ply.