Choosing the right construction material is worth careful consideration, as it can significantly impact a construction project’s success. A well-selected product will last as long as required under specific conditions and, with the right properties, can also simplify construction and reduce the amount of material needed. The choice of material can also help lower the environmental impact of construction and enhance indoor air quality and living comfort.
The choice between plywood and oriented strand board (OSB) may arise when constructing structures where either material could be a viable option, such as floors, walls and roofs. However, plywood and OSB are manufactured in very different ways, which influences their properties.
As AI is increasingly used to gather information for decision-making, we decided to test ChatGPT and Bing Chat AI by asking them about the differences between plywood and OSB board. We then shared the AI-generated answers with Riku Härkönen, Product Manager for WISA-Spruce plywood, who had the honour of telling us how well the AI information held true for WISA Plywood.
Strength and durability
AI: Plywood is stronger and stiffer than OSB due to its cross-laminated veneer layers, which enhance strength, impact resistance, and reduce splitting when nailed.
Riku: “This is accurate, and, in fact, plywood is significantly stiffer than OSB. For example, WISA-Spruce plywood has been tested to be 1.8 times stiffer than OSB/3 when looking at the material’s modulus of elasticity. The higher rigidity allows for the use of thinner panels and longer joist spans, which makes structures lighter and the panels easier to handle. For example, 18 mm thick WISA plywood is sufficient for flooring, while a similar structure requires at least 22 mm OSB, which is heavier.
“In construction, the stiffness of the material is crucial. For example, in flooring applications, it is essential to consider how much the floor will bend under load. That is why the lightweight, yet strong WISA Spruce plywood is a reliable choice for load-bearing structures.”
Moisture resistance
AI: Plywood is more moisture resistant than OSB, which tends to swell at the edges and dries more slowly. Plywood’s layered structure and higher-quality adhesives enhance its moisture resistance.
Riku: “OSB boards are indeed more prone to swelling from moisture and do not return as close to their original dimensions as plywood does. For example, when exposed to 85% relative humidity at 10°C, an 18 mm WISA-Spruce plywood panel expands by about one millimetre, while an OSB/3 panel expands approximately three millimetres. Swelling causes issues for builders, such as poorly fitting joints and loosening of fasteners.”
Versatility and workability
AI: Plywood is often easier to saw, drill and shape and is less likely to crack or tear at the edges than OSB. Nails and screws usually hold better on plywood, which is essential for strong and stable fastening.
Riku: “This is also accurate. Plywood is made from cross-laminated wood veneers, which improves its workability. OSB, on the other hand, is made from flat wood chips and may have brittle parts in its structure that can cause chipping or splintering when cut.”
Surface finishing and appearance
AI: Plywood offers a smoother and more aesthetically pleasing surface, making it a better choice for visible applications. It can also be more effectively finished with paint, stains or veneers compared to OSB.
Riku: “Beauty is in the eye of the beholder. Plywood has a natural wood grain that looks more authentic, while OSB has an industrial look. But OSB is also occasionally used for its distinct appearance.”
Availability in different categories and for different applications
AI: Plywood is available in a wide range of grades, allowing for a more precise selection based on the need – from structural applications to furniture making. In addition, special plywood, such as fire-retardant plywood and pressure-impregnated plywood, are available.
Riku: “OSB boards are available in four different use classes, and for outdoor use, they always need protection. Plywood, however, is available from different manufacturers in a wider range of grades and for diverse applications. Lightweight and strong WISA-Spruce plywood is ideal for structural applications such as floors, walls and roofs, while WISA-Birch plywood, with its beautiful surface and durability, is ideal for interior decoration and concrete forming. The range also includes special products such as the fire-retardant WISA-Spruce FR and the water-repellent WISA-Spruce WR.
“Each WISA product comes with a Declaration of Performance (DoP), which provides detailed information about the product's technical performance, such as strength, instead of just a general use class. This allows customers to verify the suitability of the product and accurately compare offerings from different manufacturers.”
Environmental impact and emissions
AI: High-quality plywood typically has lower formaldehyde emissions than OSB, which improves indoor air quality.
Riku: “The environmental impact of materials is a complex topic, and AI only addresses this partially. OSB boards have higher volatile organic compound (VOC) emissions due to their more porous structure. Additionally, they are not available with the M1 classification, which is required in Finland for materials used in public construction projects.
“WISA plywood, on the other hand, has very low formaldehyde emissions and carries the M1 emission rating. Moreover, WISA plywood products come with Environmental Product Declarations (EPDs) that describe the environmental impacts across the product’s entire lifecycle. The raw material for WISA plywood is sustainably sourced, mature wood, which has had time to bind carbon dioxide efficiently during its growth. OSB, on the other hand, is typically manufactured from fast-growing, smaller-diameter wood.
"The adhesive used in manufacturing also affects the environmental footprint of the material. Plywood contains around 3–5% adhesive, while OSB contains approximately 10% adhesives and fillers. It’s also worth noting that WISA plywood is produced with WISA BioBond bonding technology, which replaces at least 50% of the fossil-based phenol in the adhesive with lignin, wood's natural bonding agent."
Choose the material that best suits the application
As AI points out, plywood and OSB are both useful construction materials, but they differ in properties. OSB is well suited for less demanding structures, such as temporary builds or applications where appearance is not a priority.
However, if better durability, rigidity or a refined finish is required, plywood is the clear choice. Plywood’s excellent properties make it the top option for more demanding applications, such as load-bearing structures, interior decoration, and applications where better moisture resistance is required.