Mechanical performance in the event of humidification.
It is important to highlight the fact that, unlike in the case of other wood-based panels, which may « decompose », installed panels that are subject to temporary humidification will lose nothing of their mechanical properties, either during humidification or when normal humidity conditions are restored.
Wood-based products display good thermal insulation properties. Plywood’s low weight means that it boasts particularly impressive levels of thermal conductivity. Thus, for densities of between 300 and 600 kg/m3, with panel humidity at 12%, thermal conductivity in W/(m.°C) ranges from 0.11 to 0.15.
However, plywood is not an insulating material. Nonetheless, its thermal conductivity – which is 2 to 3 times lower than that of plaster board and 10 to 15 times lower than that of solid concrete – means that it actively contributes to improving thermal comfort.
A material’s acoustic properties must be analysed from three perspectives:
- Insulation against airborne noise
- Insulation against impact noise
- Acoustic correction
Plywood is often used to correct or improve acoustic comfort (concert halls, auditoriums, etc.).
While it improves insulation against airborne noise and impact noise when used as flooring, for instance, it is particularly useful for acoustic correction applications:
- It can be used as a reflecting panel, primarily to absorb bass frequencies, in which case it acts as a diaphragm
- Its excellent resonance properties can also be exploited by installing perforated panels.
It should be underlined that the care with which panels are installed is even more crucial to acoustic insulation than it is in the case of thermal insulation.
Water vapour permeability
The water vapour resistance factor of plywood, as presented in NF EN 12524, ranges from 70 to 90 (« wet-cup » testing method) and from 200 to 220 (« dry-cup » testing method) for panels with a density of between 0.5 and 0.7.
Calorific value represents the quantity of heat released by the complete combustion of a panel. Conventionally, we consider plywood to have an NCV (Net Calorific Value, which relates to the release of water in non-condensed form) equal to that of wood, i.e., approximately 17 MJ/kg at 12% humidity.
Reaction to fire represents the plywood’s capacity to help spread a fire. Like wood, of which it is primarily comprised, plywood is combustible. Depending on the application, the requirements set forth may take into account several criteria relating to this reaction to fire: flammability, contribution to fire, release of smoke and creation of burning debris.
In the case of Construction Products subject to CE marking requirements, all these criteria are taken into account for the classification of products (standard NF EN 13051-1).
A material’s reaction-to-fire class (Euroclass) is determined based on the results of tests performed according to the following standards:
- NF EN ISO 11925-2 (flammability)
- NF EN ISO 9239-1 (« Radiant panel » test for floor covering applications)
- NF EN 13823 (« SBI » test for other applications).
According to standard NF EN 13986 relating to wood-based panels for construction, plywood panels with a thickness of 9 mm or more and a density of 400 kg/m3 or more are conventionally assigned to the following class: D, s2, d0.
The fireproofing of panels allows them to be assigned to Euroclasses B or C.
Euroclasses A1 and A2 are not accessible to products made mainly from wood, given its combustibility.
Fire resistance is not a characteristic that can be directly attributed to a material such as plywood, but only to structures as a whole. The term refers to their capacity to retain their mechanical characteristics in the event of a fire, so as to enable a building’s evacuation.
In structures that contain plywood, the latter’s combustion rate can influence stability. This rate can vary between 1 and 1.2 mm/min.