Polyester generally refers to a general group of polymers (plastics) which are made from a chain of many (poly)ester groups. Specifically in commercial applications polyester refers to polyethylene terephthalate (PET). About 60% of polyester (PET) production worldwide is for the production of synthetic fibers for textile and fiber applications and another approximately 30% is used in the producing plastic bottles. Overall polyester is the third most-produced polymer in the world behind polypropylene and polyethylene. Physical properties of polyester are a very low absorption of water, low shrinkage, and high strength.

Polyester for marine covers is woven into a tight weave of fibers of a specific denier. Denier is commonly believed to describe the strength of the fabric. In reality, denier refers to the relative weight of the fabric for a specific length of the fiber. As the denier of a single fiber or yard goes up, the thickness increases. This does not always relate to the overall strength of an end fabric. The structure of the weave, and how many yarns are packed into an area plays an important role. This is measure by thread count, which refers to the actual number of threads in a square inch of fabric. A higher thread count of equal denier fiber will produce a heavier and stronger material. Some of the strongest materials use a very high amount of very low denier fibers. These fabrics like silk seem very light but are incredibly strong. Manufacturing the weave this tight is very slow and ultimately quite expensive.

For marine grade covers, fiber deniers in the range of 150 – 1200 denier are commonly used. The higher denier fiber fabrics are stronger, more abrasion-resistant and have a more rugged feel, but they are also heavier and more expensive. Marine grade polyester is also treated with UV stabilizer to extend the life in high exposure environments and is commonly coated with either PVC, Polyurethane or other coatings to increase water-resistance. These fabrics can also have different finishes applied for specific features including water-repellency, fade-resistance or other target needs.