From Scroll Saw Wiki
Typically in scroll saw work Baltic Birch plywood is used.
Baltic Birch, aka 'Russian Birch', is a popular panel best known for its light color, strength, multi-ply construction, and affordable cost.
Baltic Birch plywood typically comes in the following grades:
B----Selected one-piece face, generally light and even in color. Occasional small pin knots and some brown streaks may be allowed, but generally no patches, voids or mineral streaks. Sanded surface intended for natural finish.
BB-One-piece face generally light and even in color. Pin knots and mineral streaking or discoloration is allowed with occasional sound tight knots permitted. Open knots and defects in BB face veneers have been cut out and replaced with small oval or round veneer "football" patches before gluing. The veneer selected for the patches is of the same general color as the face veneer. Sanded surface.
CP-One-piece face very close to grade BB. Rejected from BB for small defects with more streaking. Occasional hairline splits of less than .5mm are allowed. The oval or round patches may or may not be matched for color with the base face veneer. There will normally be more patches per face than the BB grade. Sanded surface.
C---Patches, open knots and veneer splits allowed. Not sanded.