The sail can be strengthened by adding reinforcing material to the corners and stitching around the edges of the sail. Adding grommets to the corners and edges will allow the sail to be attached to the mast and spars. Because these grommets are placed through doubled material and behind the reinforcing line inside the sail edge, the resulting attachment points have tremendous strength.
The weave density of polyethylene strips in the inner layer determines the quality of the material. Common tarps have a weave of about 6 x 8. "Canopy grade" white polytarps, on the other hand, have a weave of 12 x 14 or 14 x 14. Increasingly, white polytarp is used to construct mainsails, jibs, and mizzens, while the lightweight polytarp materials are reserved for making spinnakers.
Sails made from this heavier canopy-grade white material are often called polysails. This distinguishes them from the lightweight colored polytarps available in retail stores. On the water, these sails are difficult to distinguish from traditional sails.
Polytarp is used to construct nearly every type of sail. However, the material is best for traditional sail types such as sprits, lugs, gaffs, gunters, lateens, junk sails, and jib-headed sprits. They are not suitable for sails that depend upon being highly tensioned, such as the marconi or Bermuda types of triangular sails.