Chemical-Free Treated Wood Heat-modified decking is guaranteed for 20 years by Scott Gibson A new brand of wood decking and railing components that have been thermally modified using a process developed in Finland is being marketed by Texas-based Building Products Plus. Guaranteed for exterior use for 20 years without the use of any chemical preservatives, Nature's Choice Deck is southern yellow pine that's been subjected to temperatures as high as 482ºF. According to Building Products Plus, the heat treatment - which darkens the wood - improves dimensional stability and helps the wood resist rot and decay. It also decreases moisture