some additional comments that I found.
"Stamoid is polyester fabric coated with vinyl. It is totally waterproof, light weight, stows easy and is very strong. Commonly used for hard top and t top enclosures and bimini tops. Very durable, lightweight and strong. Since it is vinyl it is easier to clean than sumbrella.Stamoid will not breath. Sumbrella will. The stamoid cover should have a couple vents built in, with the sumbrella it probably is not neccesary"Re: Seamark"The Ultimate Marine Fabric. It's an ideal combination of Sunbrella#reg;, the premier woven acrylic fabric, and Haartz textured marine-grade vinyl. The result is a rich, colorfast, waterproof fabric that stands up to the harsh conditions of any marine environment. Including salt, moisture, sun, wind and temperature extremes."Sounds like Seamark & Sunbrella Plus is the same type of product.Remember that Sunbrella is not very abrasion resistant. If you have anything rubbing on it, there is going to be some wear.