That would probably be a door skin ply ? In Sydney we have Mr Plywood which sells specialty plies including thin marine/aircraft ply. The 1.5mm is a great choice for cage lining. Kydex if it gets subjected to high heat in Summer as you might find in a locked car, will go dimply like a bad case of cellulite . I've seen a few Obsession style scopes suffering from the `fat thie' syndrome.
Rolled 1.5mm ply has a lot of inherent strength too. Monoquoque construction of rolled plywood panels is how they used to build aircraft.
