Scrim Cloth is a sailcloth made by weaving polyester or high-modulus yarns so loosely that there are visible spaces between the threads, and then laminating that open weave to a Mylar® film. The result is a material that looks almost like a window screen held in plastic – and that is exactly the point. The film carries the bias and shear loads and keeps the cloth airtight, while the widely spaced yarns carry the primary loads along the warp and fill with far less weight than a conventional tight weave. Beginners are often startled that a sail can be built from something you can see through; sailmakers know that Scrim Cloth was one of the first materials to prove that a laminate could be lighter and stiffer than any woven cloth of the same strength.
What Makes Scrim Cloth Different
A conventional woven polyester is packed with as many yarns per inch as the loom allows, then resin-finished to lock them in place. Scrim Cloth turns that logic on its head. Its yarns are spaced apart deliberately, so the cloth alone would be flimsy and porous; it becomes a sailcloth only once it is bonded to film. Because the yarns still pass over and under one another at the crossings, Scrim Cloth is technically a woven laminate, and the term is often used loosely for any open-grid reinforcement layer – but in UK Sailmakers’ usage it means this specific extremely loose weave laminated to Mylar, distinctive for the spaces between its threads.
The advantages follow directly. Less yarn means less weight per unit of strength. The film prevents the loose weave from scissoring on the bias, so stretch is low in every direction. And the open structure lets the adhesive bond film to yarn over a large area, which gives a robust laminate for its weight.
How It Is Made
The base fabric is woven on a standard loom with a very low yarn count, from polyester in the lighter styles or from aramid, Pentex or other high-modulus yarns where stiffness is the goal. It is then run through a laminator with a polyester film – Mylar is the familiar brand – and an adhesive layer, under heat and pressure, so the film bonds to the yarns and fills the spaces between them. Some styles sandwich the woven layer between two films; others add a light taffeta on one face for handling and UV protection. The finished cloth is inspected for voids in the bond, because an unbonded area is where delamination will begin.
Where Scrim Cloth Is Used
- Light-air headsails: drifters, light genoas and windseekers where every gram aloft matters and the sail is rarely flogged hard.
- Spinnaker staysails and code sails: sails that need a firm luff and low stretch at very light weights.
- Racing genoas and mainsails in the lighter wind ranges, where shape-holding beats longevity.
- Base laminates for load-path sails: a light Scrim Cloth or film-and-scrim membrane under Tape-Drive® tapes or Titanium™ fibres provides the skin while the tapes carry the loads.
Strengths and Weaknesses
Scrim Cloth is light, low-stretch and holds a designed shape with precision. Its weaknesses are those of any film laminate, sharpened by the openness of the weave. Flogging and hard creasing break the adhesive bond and craze the film; there is less yarn to protect the film from abrasion, so chafe on spreaders and lifelines shows quickly; ultraviolet light attacks both the film and any aramid yarn; and moisture trapped in a stowed sail breeds mildew between the layers. A Scrim Cloth sail should be rolled, dried, covered and never allowed to flap when a sheet would stop it.
Cruising Versus Racing
Racers use Scrim Cloth in the light-air end of the inventory and accept that a genoa built from it may hold perfect shape for two or three seasons before it is retired. Cruisers meet the material mostly in a light-air drifter or a cruising code sail, where its low weight makes a sail that will set and fill in four knots of breeze when a Dacron genoa would hang like laundry. For the working sails of a cruising boat, a heavier taffeta-protected laminate or a good woven polyester is the better choice, and a UK Sailmakers loft will say so.
Frequently Asked Questions about Scrim Cloth
Why are there gaps between the threads in Scrim Cloth?
The gaps are intentional. The yarns are spaced apart to save weight, and the Mylar film laminated over them carries the bias loads and makes the cloth airtight, so the yarns only need to handle the loads along their own length.
Is Scrim Cloth the same as a scrim laminate?
They do the same job in different ways. A scrim laminate uses straight, non-woven yarns laid between films; Scrim Cloth uses a very open woven fabric laminated to film. The names are often used interchangeably, but the construction differs.
Scrim Cloth is a reminder that a sail does not need to be heavy to be strong. Put the yarn where the load is, let the film do the rest, and treat the finished sail with the care a light laminate deserves, and it will give you the kind of shape in light air that no woven cloth can match.