what is the difference between a1 and b2 plywood?
Plywood grades of A1, A2, B1, B2 are a good two sided product and would be used where both sides are going to be seen. The back side (number grade) does have a few more blemishes than the front. ... A4, B4, C4 are a one-side-good product. The back may have open knots, filled knots, bad veneer joints or seams.