Are the Trespa panels made out of plastic?
No. Actually, it is made of 70% wood and 30% phenolic resin. Because of the great amount of wood fibers, the Trespa panels will react to temperature like wood would.
Unlike plastics, Trespa panels have a low expansion and contraction coefficient. Trespa panels can expand and contract with changes in relative humidity (just a little above 1/4” over a single panel with a 12 foot span) where as plastics expand and contract based on ambient temperature.
If within a day, temperature goes from cold to warm (ex. transition from day to night), the panels will remain stable.
If it starts to rain during a warm day, the panel will expand and contract once the sun will come out again.