Since 2000, the deck fabric has been made from Polytech, a urethane fabric. The welded urethane deck and hulls do not need any additional treatment. Clean with mild detergent and a soft scrub brush.
The Poly-Tech deck fabric begins with a 420 denier high tenacity nylon balanced weave fabric. A 4 1/2 oz. per sq. yd. urethane is applied to the topside of the fabric. The inside is coated with 2 oz. per sq. yd. of urethane. These multiple applications of urethane create a total water-barrier. The colour is provided by a colour film that is laminated to the fabric in the production process. The film has been treated with the best UV inhibitors possible. However, with the harsher UV rays of todays environment, there may be some colour shift over time. There are no additional after-market products that are to be used on the deck; there is not treatment to "bring back colour".
Prior to 2000, decks were 1000 denier nylon Cordura. This fabric has an obvious open weave, with a 1.5 ounce urethane coating on the underside. These older kayak skins, made with the nylon Cordura deck, will need to be seam-sealed and treated with a water repellent product.
Over time, the coating on the Cordura will break down. The Cordura can be treated with Scotch Guard or Nik Wax to help with the water resistance. Because the decks were sewn to the hull, seam sealing of these skins is required. Seam sealer can be applied to the underside of the deck by turning the skin inside out. The deck to hull seam needs to be sealed from the outside. (A tent seam sealer will work.)
To seam seal, have the kayak assembled. Rest on one side. Run a bead of sealer along the length of the kayak, between and on each side of the web loops, including the large web handle on each end. When dry, repeat with the other side.
Nylon Cordura will also fade after prolonged exposure to UV. There is nothing that will bring a colour back to a faded nylon deck.