I just purchased (32) 16 footers from Home Depot.It is going on steel bar joist on a dock. I did the same 20 years ago and it still look like new. The big difference I see is maybe more sawdust and less recycle plastic in the current product and yes it is coated with  of slick plastic.I assume it is to protect the fiber in it. Also thinner with radius grooves on back side to save on material.I am not using hidden fasteners. Screw thru the composite board. Worked 20 years ago !! I paid 25.93 for a 16 footer with 10 percent military discount with tax included.