What does HDO stand for in plywood?
HDO stands for High Density Overlay. It refers to a plywood panel with a high-density resin-impregnated fiber overlay bonded to one or both faces under heat and pressure. This overlay creates an extremely hard, smooth, and abrasion-resistant surface ideal for concrete formwork, signage, and industrial applications.
What is HDO plywood used for?
HDO plywood is used primarily for concrete formwork where a smooth, architectural-grade concrete finish is required. The hard overlay surface produces clean off-form concrete with minimal finishing needed. Other common uses include highway signs, industrial work surfaces, and marine applications where a durable, moisture-resistant panel is essential.
Is HDO plywood waterproof?
HDO plywood uses BWP (boiling waterproof) phenolic adhesive throughout its core and a resin-saturated overlay on the face, making it highly water-resistant. While no wood product is truly waterproof indefinitely, HDO panels resist moisture penetration far better than standard plywood. Sealing cut edges and maintaining the overlay surface extends its performance in wet environments.
What is the difference between HDO and MDO plywood?
The key difference is overlay density and surface finish. HDO has a harder, denser overlay (typically 60+ lb resin content per 1,000 sq ft) that produces a glossy, smooth surface ideal for exposed concrete. MDO has a lighter overlay (40–50 lb) that produces a matte, paintable surface suited for signage, siding, and moderate-finish formwork. HDO typically costs more but delivers more reuse cycles in formwork applications.
