Fabrics that hold up well to abrasion are generally preferred for marine and outdoor cover applications. A rating of 3 or greater is considered very good. Abrasion resistant fabrics are usually heavy, stiff, and often coated with vinyl or other resins which make their surfaces somewhat harsh. A few exceptions, like Cotton Duck and Sunbrella Furniture Fabric, are able to maintain a level of suppleness to their surface. Although Sunbrella Marine Grade was given a rating of 2, it is still the most popular and widely used outdoor canvas in the United States. Abrasion resistance can be built into a cover made with Sunbrella by adding extra layers or reinforcement patches to areas prone to abrasion.