Coated Fabrics and Tarpaulins: How Much of the Weight Is Coating?

A coated fabric is two materials sold as one: a textile base cloth, usually woven, and a layer of polymer spread or laminated over one or both faces. Tarpaulins, truck curtains, inflatable boats, marquee roofs, faux-leather upholstery, rainwear and bag fabrics are all built this way. When you compare coated fabrics, the headline weight hides a split that matters: how much of the cloth is the textile that gives it strength, and how much is the coating that keeps water out. This guide explains the common coatings, shows how to read a coated fabric's weight and yarn figures, and works through a tarpaulin example with the site's Fabric Weight Converter, Fabric Weight from Dimensions and yarn count converter.

The base cloth and the coating do different jobs

The base cloth carries the load. Its yarns, weave and density decide the tear and tensile strength, how much the fabric stretches, and how well it holds stitches or welds. In heavy coated fabrics the base is often a polyester woven or a scrim, an open grid of yarns that the coating fills in.

The coating keeps out water and wind, resists abrasion and ultraviolet light, takes printing, and in some products adds flame retardancy. On its own a coating film is weak and tears easily; on its own an open scrim lets everything through. Together they make a fabric that is both strong and impermeable.

Common coatings

• PVC (polyvinyl chloride). The usual coating for heavy tarpaulins, truck curtains, marquees and banners. Heavy, tough, weldable with heat or high-frequency equipment, and easy to print.
• Polyurethane (PU). Common on rainwear, bags, tent floors and faux leather. Lighter and more flexible than PVC. Some PU coatings break down slowly with heat, humidity and age, which shows up as peeling or a tacky surface on old gear.
• Silicone. Used on lightweight nylon and polyester for tents and tarps, often called silnylon or silpoly. Very water-repellent and slippery, but hard to glue or seam-tape.
• Acrylic and other finishes used as lighter coatings on awning and outdoor furnishing fabrics.
• Fluoropolymer and similar finishes that make a surface repel water and dirt without forming a continuous layer. These are finishes rather than coatings in the strict sense, and some older chemistries are now restricted or being phased out in a number of countries.

Reading a coated fabric's spec

A data sheet for a coated fabric usually gives:

• Total weight in g/m² or oz/yd². This normally includes the coating.
• Base cloth: fibre, yarn linear density (often in dtex or denier), and construction, such as 1000 x 1000 denier, 9 x 9 yarns per centimetre.
• Coating: polymer and sometimes the coating weight per square metre on each side.
• Tensile and tear strength, adhesion of the coating to the base, and any water-pressure or flame-test results.

Yarn figures for heavy base cloths are coarse. In the yarn count converter, a 1000 denier yarn is 111.11 tex or 1111.11 dtex, a 600 denier yarn 66.67 tex, and a 420 denier yarn 46.67 tex. Converting to tex makes it easier to compare a European data sheet that uses dtex with an Asian or American one that uses denier.

Worked example: how much of a heavy tarp is coating?

Suppose a heavy PVC tarpaulin fabric is listed at 650 g/m². The converter gives 19.17 oz/yd² and puts it in its Very heavy band. Now suppose, for illustration, the data sheet says the polyester base cloth weighs 220 g/m² before coating. The coating then accounts for 650 − 220 = 430 g/m², about 66% of the total weight.

That ratio is typical of the idea rather than of any particular product, and real proportions vary a great deal. But it makes an important point: in a heavy coated fabric, most of the weight you pay to ship and lift is not the part carrying the load. Two tarps of the same total weight can differ a lot in strength if one has a heavier base cloth and a thinner coating.

Weight of a finished tarpaulin

Using the dimensions tool on a 4 m by 6 m sheet:

• At 650 g/m²: 24 m², weighing 15.6 kg.
• At 250 g/m², closer to a medium-duty woven polyethylene tarp: the same 24 m² weighs 6 kg.

Hems, eyelets, ropes and welded seams add to both. The difference explains why heavy PVC sheets are reserved for jobs that need them, such as truck covers and long-term outdoor use, while lighter sheets are used for occasional cover. It also matters for anyone rigging a cover overhead: a wet, heavy sheet puts real load on its fixings and on whatever it is tied to.

Coated fabrics for upholstery and clothing

Faux leather and vinyl upholstery are coated fabrics too, typically a knitted or woven base with a PU or PVC surface embossed with a grain. When comparing them:

• A knitted base stretches and wraps curved furniture more easily; a woven base is more dimensionally stable.
• The total weight tells you little about how long the surface will last. Abrasion test results, often quoted as rub counts by a stated method, are the better guide for seating.
• Domestic upholstery in some countries must meet fire-safety rules, and the coated fabric and the filling are assessed together. In the UK, for example, furniture fire-safety regulations apply to upholstered furniture sold for use in the home. Check what applies where you are before re-covering furniture for sale.

For coated clothing fabrics, breathability matters as much as waterproofing. Solid coatings that block water also block water vapour, which is why breathable rainwear uses microporous or hydrophilic coatings and membranes. The guide to waterproof fabrics and their ratings covers that side.

Sewing and working with coated fabrics

• Every hole is permanent. Pins and unpicked stitches leave holes that will leak. Use clips, and test stitch length on a scrap.
• Use a suitable foot. A Teflon, roller or walking foot helps PVC and PU feed without sticking.
• Seal the seams if the item must keep water out: welded seams, seam tape compatible with the coating, or a seam sealer.
• Do not iron the coated face. Many coatings soften or melt at ironing temperatures.
• Allow for stiffness in yardage. Heavy coated fabric does not ease or drape, so pattern pieces need accurate cutting and hems need room to fold.

Care and lifespan

Most coated fabrics should be cleaned with mild soap and water and dried naturally. Machine-washing, solvents and high heat can crack or delaminate the coating. Store them dry: a tarp folded away wet can grow mildew on the base cloth even when the coating itself is intact. Ultraviolet light slowly degrades most polymers, so outdoor covers have a working life measured in seasons or years, depending on the product and the climate.

Fire safety

Many coated fabrics burn, and some PVC and PU coatings give off harmful smoke when they do. Flame-retardant grades exist and are required for many uses, such as marquees and temporary structures for public events, stage drapes, and some vehicle and building applications. If a coated fabric will be used where people gather, near heat sources, or in a regulated product, buy a grade certified to the standard your local rules require and keep the certificate. Do not rely on a seller's description alone, and do not put any coated cover close to a heater, barbecue or flame.

What the tools cover, and what they do not

The converter and dimensions tool handle the arithmetic: total weight in either unit, the weight of a sheet of any size, and the yarn conversions for the base cloth. They cannot tell you how a given weight splits between base and coating unless the data sheet does, and they say nothing about strength, adhesion, ageing or fire performance. For those, rely on the manufacturer's tested figures and, where safety depends on it, on certification to the relevant standard.