Thermowood Redwood D = Durable WOOD. Thermo Wood is actually a process, not a species, but it’s now just commonly referred in the trade as a species given its ubiquity. The process modifies the timber using very high temperature and steam in a controlled chamber so that the cell structure is changed and the end product is more stable and slightly more durable (albeit a bit more brittle too). The most common species is Pine. Thermowood can be used for both cladding and decking so is this profile which is smooth both sides with small eased edges. Thermowood is a durable product which takes wood finishes e.g oils and coatings well if required. Thermowood can be face fixed with screws to the face to avoid splitting during drilling.