PVC Tarpaulins and Lorry Covers: The Coat Weight Nobody Checks Until the Second Winter

The first tarpaulin order I ever looked at closely came with a spec sheet of exactly one line: "PVC coated fabric, 610 gsm, 1000D." The buyer had bought the same thing from the same trading company for six years. Then a competitor started undercutting him by 18% on the same stated weight, and he asked me to find out why. The answer was on a lab bench in Nantong, roughly forty minutes after we started cutting samples.

Chinese PVC tarpaulin is genuinely good value. Nantong, Haining and the fabric belt around Linyi produce a serious share of the world's truck covers, tent cloth, hay tarps and billboard substrate. The problem is not the industry. The problem is that "gsm" is one of the loosest numbers in Chinese textile trade — it describes the finished roll, not what's on the polyester.

What the gram weight actually adds up to

A coated tarpaulin is a sandwich: base fabric, coating on both faces, and whatever fillers the formulator decided to put in the plastisol. On a 610 g/m² fabric with a woven 1000D base, you might have 230-260 g/m² of base cloth and 350-380 g/m² of coating split between the two faces. On a cheap roll, part of that 350 g is calcium carbonate. Calcium carbonate is not illegal, it's not even unusual, and it does make the sheet feel heavier and stiffer. What it doesn't do is resist flexing, UV or cold.

The practical consequence: two rolls both reading 610 g/m² can differ by three or four years of service life on a truck side curtain that gets rolled and unrolled twice a day. You will not see it in the first year. You see it in year two when the fold lines go white and start cracking.

When you ask a Chinese factory for tarpaulin samples, ask for the base fabric specification separately — yarn denier, warp and weft density, weight of the greige cloth — and then ask for the coating weight per side. A decent factory can answer in a day because it has the formulation sheets. A trading company will send you another photo of a roll.

The four tests that actually predict failure

You don't need a full laboratory. Four cheap checks cover most of the risk on a truck cover or hay tarp order.

Cold fold. Put a 100 × 100 mm sample in a domestic freezer at −20 °C for four hours, then fold it back on itself once, firmly, and look along the crease with a light behind it. A properly formulated DOP or DINP plasticised PVC survives this. A heavily filled sheet whitens and shows micro-cracking at the fold. This one test has saved me more money than every lab report combined.

Weld peel, not glue. High-frequency welding is the standard joint for tarpaulins, and its strength is set by the plasticiser level as much as by the machine setting. Ask for welded lap joints at 30 mm and pull them. A good weld fails by tearing the fabric next to the seam. A bad one peels cleanly off the coating. If a supplier offers solvent-glued seams on a truck cover, that tells you what their welding line looks like.

Tear strength, trapezoidal, warp and weft. A 610 g/m² fabric should be sitting in a recognisable band; if the numbers are dramatically low relative to the stated weight, filler is the first explanation.

Colour and gloss after weathering. You cannot do a two-year outdoor test on a sample, but you can ask for the factory's own xenon-arc or QUV data on the exact lacquer topcoat they propose, and then ask whether the topcoat is the same on the sample as on the bulk roll. It's a surprisingly common switch: glossy lacquer on the A4 swatch, matte or no lacquer on the roll.

Translucent and light-colour stock is the hard part

If you want a white or pale grey truck cover, or a translucent roof sheet for a tent, the difficulty goes up substantially. White titanium-dioxide pigmented PVC reflects UV better but shows every migration stain, every roll mark and every drop of plasticiser bleed. Off-white batches differ visibly between production runs, and the difference is much more obvious on a large flat sheet than on a small swatch.

For any pale colour, ask for a retained master swatch signed off before production, hold it for the life of the order, and put the acceptance condition into the purchase order as a ΔE limit measured under D65. On large format tarpaulin, ΔE 1.5 is achievable but you have to specify it, because the default is "looks white".

Widths, roll lengths and the shipping consequence

Most Chinese PVC tarpaulin coating lines run around 1.6 m to 3.2 m of usable width. Truck side curtains and container covers are usually made by welding panels, so a wider base fabric means fewer seams and fewer failure points. If your design needs a 2.6 m finished width, tell the factory up front — a 1.6 m line will give you a welded seam right where the cover flexes most.

Rolls on a 40HQ: a 600 g/m² fabric at 2.5 m wide, 50 m per roll, weighs about 75 kg without core, so 24 rolls fits comfortably inside the weight limit and you will cube out long before you run out of tonnage. That means freight is priced on volume, not weight, and the packing pattern matters more than the per-kilo price. Ask for the roll diameter and the pallet drawing, not just the roll length.

What to put in the purchase order

• Base cloth: yarn denier, warp/weft density, greige weight per m².
• Coating: total and per-face gram weight, plasticiser type, presence and maximum percentage of filler.
• Topcoat: lacquer type, gloss level, and a statement that the topcoat on bulk equals the topcoat on the approved swatch.
• Cold fold at −20 °C, pass/fail, per production lot.
• Weld strength on 30 mm lap joints, pull test, result recorded.
• Colour: master swatch retained by both sides, ΔE limit under D65, measured on each lot.
• Roll: width tolerance, length tolerance, core diameter, and whether splice joints inside a roll are permitted. A splice in the middle of a 50 m roll is fine for a ground sheet and catastrophic for a printing line.

None of that is exotic. It is the standard spec that a serious Chinese coating factory already works to for its European industrial customers. The only thing that changes when you write it down is which factory quotes you.