The reason is all vinyls are rated by hours outdoors. Normally 1500 hrs outdoors is pretty standard which amounts to about 100 days if you only count daylight hours. Makes it seem kind of silly to put vinyl on anything that’s going to be outdoors.
Vinyl will always crack and fall apart eventually if it is exposed to temperature extremes and or UV. That’s why Sunbrella™ was invented. It has been the gold standard in outdoor fabric for more than forty five years.
Sunbrella™ is manufactured by Glen Raven Mills here in the USA. Made from acrylic fiber woven into a canvas like fabric it offers the breathability of canvas without the shrinkage, rotting or fading. One of the great advantages of breathable fabric is that it does not trap moisture in like vinyl where it can grow mildew. If rigid foam hot tub covers smell like mildew, the vinyl on the outside is one of the reasons why. Since acrylic is the same stuff most spas are made of Sunbrella™ is incredibly durable.
Sunbrella™ doesn’t crack in cold like vinyl, or fade like canvas. If you live near a marina every boat top you see out there in a bright color is Sunbrella™. Anything else would fade out quickly, even the paint on the boat will fade before the Sunbrella™ will.
Years ago a neighbor came in and wanted us to repair his sail cover. His sail cover had been on his sail boat for twelve years, through all the weather the northwest pacific coast could through at it. For those of you who don’t know sailing, the typical sail material needs to be protected from exposure when not in use so it is bundled and covered with a sail cover. The sail cover is the shield that covers the expensive sail from damage.
Our neighbors sail cover was made from Sea Grass Green Sunbrella™ which is a bold, fairly bright green. We explained to him that if it were patched the cover with new material it would look terrible because new bright material would stick out like a sore thumb on the faded older material. We laid a piece of new material on his old cover to prove the point.
To our astonishment the only difference between the two was his was a little dirty. Once it was cleaned and patched, there was no difference between the new fabric and the old even after constant exposure for twelve years. If your spa is outdoors and your tired of replacing spa covers due to sun damage you really need to get the only spa cover that is offered in Sunbrella™ fabric the SpaCap.