Trex is a composite of recycled plastics and wood; the company has been making decking products for 20 plus years. The early products molded terribly, but the addition of a PVC-type coating on three sides has helped solve the mold problem that riddled early versions of the product. Ground level Trex decks can still mold (black) on the bottom, the side where the wrapper is absent.
Azek is a pure PVC – it’s lighter and the only mold issue would be surface green mold which grows on any surface in the right conditions. Azek is lighter and doesn’t mushroom or split near the edges. Trex can be installed without this happening, but it takes more effort.
Both companies make quality products, but I generally prefer the Azek product line for my projects. Sometimes color choice and price can be a big factor in deciding which product to choose. The high end of the price range of both products are similar, but Trex does offer a lower priced product.
I hope this helps educate those considering a Trex or Azek deck. I always recommend customers take a look at both products before deciding. Azek products can be seen at AWD on Chamberlain Ln and Trex at K&I on Collins Lane, or – of course – there websites:
Have a good one!