Wayne's right about true Baltic Birch and it is expensive. I'm cheap and a wholesaler was 45 miles away so I looked for something else.This is the plywood I used. It's very much like the late, lamented Marine Plywood every lumberyard, pre-Big Box, used to carry.
It is 7-ply with an "A" side, no visible voids on any of the cut pieces and nary a rattle.