Baltic Birch is not a specific species of birch, but is a general designation of plywood from Russia and nearby Baltic states (such as Finland). As with any natural wood product, quality can be variable. However, Baltic Birch plywood is generally regarded as being of higher quality than standard birch plywood.
In a nutshell, Baltic Birch plywood is made entirely from birch plies, with no softwood or filler plies in the center. Furthermore, the plies themselves tend to be much thinner, allowing for more plies for a given thickness, and greater stiffness and stability.
Baltic Birch grades
The grading for Baltic Birch is established by the Russian intergovernmental standard GOST 3916.1-96.
Grading is given as the two outer faces of the plywood, in the format of [front/back]. For instance, baltic birch with a “B/BB” grade would have a B grade front ply, and a BB grade back ply.
A: Nearly perfect and flawless face veneer ply. This grade is no longer available commercially. (Also designated grade “E” according to GOST 3916.1-96.)
B: Generally uniform light color, with no plugs, or open cracks/splits. A limited amount of pin knots, and minor color inconsistencies are allowed. (Also designated grade “I” according to GOST 3916.1-96.)
BB: Generally uniform color, though color variations/stains are allowed. Limited amount of plugs, cracks/splits, and unlimited amount of pin knots allowed. (Also designated grade “II” according to GOST 3916.1-96.)
CP: Generally less consistent color, more prevalent defects (knots, staining, etc.), and an unlimited amount of plugs. (Also designated grade “III” according to GOST 3916.1-96.)
C: Utility grade; inconsistent color with mineral staining, cracks/splits, larger knots, etc. (Also designated grade “IV” according to GOST 3916.1-96.)