To be clear its usually found on the exterior of the top of the sauna. Plywood is made from synthetic adhesives and cured in formaldehyde. I have only found in all my research a handful of brands that do not use plywood and are actually the same wood type as advertised all the way through the sauna. If a company tells you they are using Luan wood that is also another fancier version of plywood so don’t be fooled.

Read more about that here: http://homeguides.sfgate.com/luan-wood-99466.html

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