Strapping Buying Guide: Steel vs. Polyester vs. Polypropylene, and When Cord Strapping Wins

Most strapping gets specified off one number: break strength. Then a pallet arrives with the straps hanging loose, or a steel strap snaps when the load settles, and the response is to buy something heavier. Usually the strap was strong enough. It was the wrong material for how the load behaves.

The question that decides strapping is not how much load it will hold before it breaks. It is what the load does after you tension it.

The four materials at a glance

	Polypropylene (PP)	Polyester (PET)	Steel	Cord (woven or composite polyester)
Break strength, typical	130 to 1,000 lb	425 to 3,000 lb	665 to 5,500 lb	350 to 7,700 lb
Stretch under tension	High	Moderate	Almost none	Low to moderate
Holds tension over time	Poorly, relaxes within hours	Well	Well on rigid loads, fails on settling loads	Well, and can be re-tightened
Joint	Seal and crimp, heat or friction weld	Friction weld, or seal and crimp	Crimped seal, notch or push type	Wire buckle
Edge safety	Safe	Safe	Cuts, recoils when cut	Safe
Cost per foot	Lowest	Low to mid	Highest	Mid to high

Polypropylene: cheap, stretchy, short-term

Polypropylene is the lightest and cheapest strapping and it stretches the most. That stretch is useful for a few hours: it lets the strap absorb a bump without breaking. The problem is that PP does not recover. Tension it, and it starts relaxing almost immediately. By the next morning a strap that was tight is measurably slack.

That makes it right for bundling, closing cartons, unitising light loads for a short trip, and anything strapped by machine at high volume where the strap is doing a light job for a short time. It is wrong for a pallet going three days on a truck, and wrong for anything in a hot trailer, because heat accelerates the relaxation.

Hand grade vs. machine grade. Hand grade is thicker and comes in heavier break strengths (300 to 1,000 lb in the sizes we carry) for use with a manual tensioner and sealer. Machine grade is thinner, wound to feed through automatic and semi-automatic strappers, and generally 130 to 500 lb. They are not interchangeable: machine grade in a hand tool slips, and hand grade will jam a strapper.

The mistake: buying 1,000 lb polypropylene for a heavy pallet because the number looks like the polyester number. Break strength is the same; retained tension is not. The pallet arrives loose.

Polyester: the default for pallets

Polyester is what replaced steel on most pallet loads. It stretches less than polypropylene and, more importantly, it recovers: when a load settles or compresses in transit, the strap pulls back and stays tight. It holds most of its applied tension for days, which is what you want on anything that ships.

It is the right choice for palletised product, bricks and block, lumber, corrugated, cans and bottles, and any load that compresses or settles. Its limits are sharp-edged loads and very high heat, where steel still wins.

Smooth vs. embossed. Smooth polyester feeds cleanly through machines and friction-weld tools. Embossed polyester has a textured surface that grips better in a crimped seal and on a rough load, and it is the safer choice with hand tools and serrated seals. Waxed coils feed more reliably in machines; the AAR grade meets the Association of American Railroads spec for rail shipments, and if your customer ships by rail they will ask for it.

The mistake: sizing the strap and ignoring the joint. A polyester strap is only as strong as its seal. A friction weld from a battery tool holds most of the strap's break strength; a crimped seal on a manual tool holds noticeably less, and a badly crimped one holds very little. If you are stepping up in break strength, check that the tool and seal can actually deliver it before paying for the heavier coil.

Steel: strongest, stiffest, least forgiving

Steel has the highest break strength per width and essentially no stretch. That is exactly what you want when the load is rigid and does not move: steel coils, structural steel, bundled pipe, machinery, anything with edges that would cut through plastic, and anything that sees heat.

It is also exactly why steel fails on the wrong load. Strap a stack of corrugated or lumber with steel, let it settle a quarter inch in transit, and the strap is now loose with no way to take up the slack. On a load that expands, the same stiffness means the strap breaks rather than gives. This is the one that fools people: steel is not the safe choice just because it is the strongest.

Regular duty vs. high tensile. Regular duty is the general-purpose grade. High tensile is heat-treated for higher break strength at the same size and, more usefully, it tolerates shock and shifting better. If the load moves in transit at all, high tensile earns its cost.

Finish and wind. Painted and waxed is the standard finish; the wax lets the strap slide through the tensioner and lets seals crimp properly. Oscillated-wound coils are the production standard. Ribbon-wound coils, and the small portable coils in a self-dispensing carton, are for shops that strap a few loads a day and do not want a 100 lb coil on a dispenser.

Seals. Open (notch) seals are the standard and need a sealer that notches the joint. Full-overlap push seals are used where the strap is tensioned and sealed in one motion. Use the seal grade that matches the strap grade; a regular duty seal on high-tensile strap is the weak point in the system.

Steel springs when it is cut and the edges are sharp. It needs gloves, eye protection and a proper cutter, and if your people are not using them, that is a reason on its own to look at polyester.

Cord strapping: the one people forget

Woven and composite polyester cord strapping is polyester yarn woven or bonded into a flat strap, joined with a wire buckle rather than a seal. It is applied with a simple tensioner, needs no sealer or welder, and the buckle can be released and re-tightened.

That last point is what makes it different. On a load that settles, or a bundle that is opened and re-closed, cord can be re-tensioned in place. It is soft on painted and finished goods, it does not rust or stain, it holds tension well, and heavy-duty grades reach break strengths steel would need a wide strap for. Lumber, pipe, bundled goods, container lashing and anything with a finished surface are its natural jobs.

The mistake: matching the buckle by width only. Wire buckles are sized to the strap's width and break strength together. A light buckle on a heavy strap will open before the strap breaks.

Choosing

• Cartons, bundles, light loads, short trips, high volume: polypropylene, machine grade if you run a strapper, hand grade if you do not.
• Pallets that ship, loads that settle or compress: polyester. Smooth for machines and friction-weld tools, embossed for hand tools and crimped seals.
• Rigid loads, sharp edges, high heat, rail and heavy industrial: steel, high tensile if the load shifts.
• Anything that needs re-tightening, finished surfaces, lumber and pipe, no sealer available: cord.

On width: go wider before you go thicker if corners are being crushed, and use edge protectors rather than a stronger strap if the strap is cutting in. For most pallet work, 1/2" and 5/8" polyester cover the range.

Where Supply Tie fits

Our strapping line is PAC Strapping. In the strapping collection that means:

• Hand-grade polypropylene in 1/2" and 5/8", 300 to 1,000 lb, and machine-grade polypropylene from 1/4" to 1/2", including 5 mm strap for Mosca and EAM machines.
• Smooth polyester from 1/2" to 1" and 500 to 3,000 lb, embossed polyester from 3/8" to 3/4" and 425 to 1,900 lb, in green and black, waxed, and AAR grades.
• Steel strapping coils in 1/2" to 1-1/4", regular duty and high tensile, oscillated and ribbon wound, up to 5,530 lb, plus 300 ft portable coils in a dispensing carton and a 3/4" x 0.020" coil sold singly.
• Regular-duty and heavy-duty woven cord and composite cord from 1/4" to 1-1/2", 350 to 7,700 lb.
• Plastic seals in open, long and combination styles, and steel seals in open and push types, regular and heavy duty, by the case.

Most coil products are priced by the pallet with a per-variant minimum shown on the page; seals and portable steel are by the case or coil. Custom sizes, finishes and tensioner and sealer tools go through the request-a-quote listings in the same collection.

If you are not sure which material or width your load wants, tell us what you are strapping, how far it travels and whether it settles, and we will spec it.

Those request-a-quote listings are here: polyester and polypropylene strapping, and steel strapping.