| Exterior Structural Plywood | EN 636-3 for exterior conditions; other regional structural plywood standards may apply | 9–25 mm | Cross-laminated veneers, good strength-to-weight ratio, relatively stable panels, clean cutting and fastening | Designed for exterior exposure when correctly manufactured and finished; exposed edges still require sealing | Suitable for many sheathing, bracing and panel applications when thickness, span and grade are correctly specified | Wall and roof sheathing, soffits, exterior cabinetry, doors and covered outdoor structures | Quality varies by veneer grade and face classification; it must not be assumed to resist insects or decay without preservative treatment |
| Marine Plywood | Often manufactured to marine plywood requirements such as BS 1088 or equivalent regional specifications | 6–25 mm | High-quality veneers, durable bonding, low core void content and good dimensional consistency | Very good resistance to repeated wetting when properly specified, sealed and maintained | Strong and stable, but design values must come from the product declaration or applicable structural standard | Boatbuilding, exposed joinery, high-quality outdoor furniture and demanding wet-area construction | Marine grade describes construction and bonding quality, not automatic resistance to termites, fungi or permanent immersion |
| Pressure-Treated Plywood | Must comply with the applicable treated-wood and structural plywood requirements in the installation region | 9–25 mm | Structural plywood with preservative chemicals introduced under pressure to improve biological durability | Better resistance to decay and insects than untreated panels, provided the treatment reaches the required retention and penetration | Can be structural if the untreated panel grade and treatment process are both approved for the intended use | Decking components, outdoor utility structures, landscaping, foundations and locations with increased decay risk | Cut edges and drilled areas may need field treatment; fasteners must be compatible with the preservative system |
| OSB/3 | EN 300, load-bearing boards for use in humid conditions | 9–22 mm | Engineered strands arranged in oriented layers; uniform panel structure and efficient material use | Suitable for humid service conditions, but not intended for unprotected, permanently wet exposure | Load-bearing in humid conditions when the declared span, thickness and edge-support requirements are followed | Roof decking, wall sheathing, floor substructure and protected exterior construction | Edges can swell after prolonged wetting; it requires adequate ventilation, drainage, joint gaps and weather protection |
| OSB/4 | EN 300, heavy-duty load-bearing boards for use in humid conditions | 12–25 mm | Higher mechanical performance than OSB/3, with oriented strands and strong directional properties | Performs in humid conditions but is not a substitute for a fully weatherproof exterior cladding system | High load-bearing capacity for demanding structural applications, subject to engineering design and product data | High-load roof and wall sheathing, platform floors and heavily loaded timber-frame assemblies | Usually heavier and more expensive than OSB/3; swelling and dimensional movement must still be controlled |
| Exterior-Grade MDF | Use only products specifically classified for exterior or severe-humidity service under the relevant local standard | 6–30 mm | Fine, smooth fiber surface; easy to machine, rout and paint; generally heavier than plywood | Special exterior formulations resist moisture better than standard MDF, but all faces and edges need a durable coating system | Generally non-structural unless a product is specifically tested and declared for structural use | Painted trim, signage, decorative panels, molded profiles and protected exterior furniture parts | Not suitable for structural sheathing by default; prolonged water exposure can still cause swelling and edge damage |
| Exterior-Grade Particleboard | Only use panels explicitly classified for exterior or severe-humidity conditions | 10–25 mm | Flat, economical engineered panel with relatively uniform surface and lower screw-holding performance than plywood | More vulnerable to edge swelling and loss of integrity than plywood when water enters the panel | Usually limited to non-structural or specifically engineered applications | Protected exterior cabinets, temporary installations and covered applications with complete surface sealing | Generally a poor choice for exposed cladding, wet ground contact or applications requiring high fastener strength |
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