Plyform is a plywood product specially made for concrete formwork. Plyforms are available in class I and class II, where class I is stronger than class II. Other plyform that is commonly used for formwork includes B-B plyform, high-density overlaid (HDO), and structural 1 plyform.
Plywood and plyform have particular orientations that affect their strength. A weak position can be achieved when the grain (face grain) is parallel to the span of support. A stronger orientation is seen when the grain (face grain) is perpendicular to the span of support (Figure 1.6).