Strapping: PP, PET or steel, and when to use each

A strap has one job. It squeezes the load so that it moves as one block.

How hard it squeezes on the day we pack is easy to see.

How hard it is still squeezing after a week on the road, or three weeks at sea, is the real difference between PP, PET and steel.

My short answer is this. Use PP for light cartons and bundles that do not travel far. Use PET for heavy pallets, bricks, timber, loads that settle, and most export work. Keep steel for very heavy, rigid loads, sharp edges that would cut plastic, and hot products such as coils fresh from a mill.

If I could give a purchase team only one rule of the trade, it would be this. Do not compare straps on break strength alone. Compare how much tension each one keeps, and how strong its joint is.

What each strap is

1. PP (polypropylene) strap is the light, cheap plastic strap used on cartons, newspaper bundles and light pallets. It stretches the most.
2. PET (polyester) strap is stiffer and much stronger than PP for the same size. It is the usual alternative to steel.
3. Steel strap is flat, cold-rolled steel. It is the strongest and stretches the least.

There is also a fourth kind we meet in container work: composite or corded polyester strap. It is polyester yarn in a coating, closed with a steel buckle, and it can be re-tensioned. Cordstrap, for example, sells it for container cargo.

Strength: what the Indian standards say

BIS has a separate standard for each material. I find it useful to put one size side by side, so let us take a strap about 12 mm wide and 0.5 mm thick.

So for the same width and thickness, PET is roughly twice as strong as PP, and good steel is more than twice as strong as PET.

That does not make steel twice as good. IS 10106, the Indian packaging code for tensional strapping, warns that steel and plastic strap cannot be compared meaningfully on strength alone, because plastic strap works through its stretch as well as its strength.

Outside India, the references are ASTM D3950 for plastic strapping and joining methods (2023 edition) and ASTM D3953 for flat steel strapping and seals (2015, reapproved 2022). Europe uses EN 13394 for plastic and EN 13246 for steel.

Stretch and tension: the number that actually holds our load

Every load we ship moves a little in transit. Cartons compress, bags settle, and timber dries and shrinks. When our load gets smaller, the strap has to shrink with it, or it goes slack.

This is where the three materials really differ. Cyklop's strapping brochure (2022) gives these typical figures.

Think of the charpai many of us grew up sleeping on. Its woven rope gives a little when we sit and springs back when we stand. That springing back is elastic recovery, and it is what keeps a strap tight on a load that settles.

1. Steel barely stretches, so it holds a rigid load very firmly. If the load shrinks even a little, steel goes slack and stays slack.
2. PET stretches a little and recovers well. EAM-Mosca's plastic strapping guide (read October 2026) says PET keeps its initial tension longer than PP. The foreword of IS 15559 also credits PET's elastic memory for long-term retained tension.
3. PP stretches the most. It absorbs knocks well, but it gives up tension faster.

The makers do not fully agree on PP, and I would not hide that from you. Some sell its elastic memory for loads that shrink, while Fromm describes PP as having low retained tension. The European Commission's 2014 cargo securing guidelines say PP, PET and PE straps all tend to lose tension over time.

My own reading is simple.

For a short trip with light cartons, PP is fine. For anything heavy, long or by sea, I would start with PET.

Which strap for which load

I would pin this table up in any dispatch area.

Joints: the weakest point of every strap

A strap is only as strong as its joint. When a strapped load fails, the joint is the first place I would look.

IS 10106 lists the joint types: a separate seal crimped or notched onto the strap, seal-less joints cut into the strap, heat welding, friction welding, buckles and tying. It also gives a guide. The joint should generally hold at least 50% of the strap's strength for plastic strap and 65% for steel.

The method matters a lot with PET. Fromm Packaging Systems explains (November 2023) that a metal seal on PET usually holds less than half of the strap's strength. A joint above 75% of break strength counts as efficient, and friction welds often do better than that. All battery tools use friction welding.

So a cheap seal can throw away half of the expensive PET we paid for.

Tools, briefly

1. Manual tools. A tensioner pulls the strap tight and a sealer crimps the seal. They are simple and cheap, but the tension depends on the person.
2. Battery tools. These tension, friction-weld and cut in one go, at a set tension. Steel needs its own tools.
3. Semi-automatic machines. The operator feeds the strap and the machine tensions, seals and cuts.
4. Automatic machines. A fixed arch guides the strap and the machine runs the whole cycle.

Whichever we use, the tension has to suit the load. The Commission's guidelines say straps should be tensioned very well, and IS 10106 asks for enough initial stretch to make up for the elasticity of plastic strap.

Protect the corners

A tight strap on a carton edge cuts in. The 2014 EU guidelines say straps often damage products unless suitable corner protection is used, and IS 10106 asks for edge protectors or pads under the strap. It specifically recommends paperboard pads under steel strap on fibreboard cases.

Corner protection helps twice, because it protects the strap as well. It spreads the force and stops sharp edges cutting plastic strap during tensioning. Our guide to edge protectors and corner boards covers sizes and types.

Safety: cutting a strap is the dangerous moment

A tensioned strap is stored energy. When we cut it, it flies outward. Signode's instructions for its strap cutters and the UK HSE's guidance on metal stock agree on the basics, and I would make each one a site rule.

1. Wear safety glasses with side shields, and gloves. Steel strap edges are sharp.
2. Stand to one side of the strap when you cut it, and keep others away. A compressed load makes the strap recoil much harder.
3. Use a proper strap cutter. Signode says never to use a claw hammer, crowbar, chisel or axe, because the strap will fly apart with dangerous force.
4. Cut square. A strap cut at an angle leaves a much sharper end.
5. Pick up cut strap at once. Loose banding on the floor trips people and cuts ankles.
6. Never lift a load by its straps. Strap is not a lifting aid.

Point 6 is not theory. The HSE's guidance on storing steel stock (HSG246, second edition) describes a stack of steel bundles that collapsed on two workers when the banding on one bundle failed. The possible cause it names is an unsafe lifting operation using the banding itself.

PET has one safety advantage here. The IS 15559 foreword notes that it has no sharp edges, and Mosca says it snaps back less than steel when cut.

When strapping is the wrong tool

We sometimes ask strapping to do jobs it cannot do.

1. Small, loose or irregular items. A strap holds only what it touches, and a carton between two straps can still slide out. These loads need stretch film or a box, and our guide to stretch film covers wrapping.
2. Weak cartons stacked high. Tight straps crush the top cartons, so use corner boards, or lower the tension and add film.
3. Securing a pallet to a truck or inside a container. Strapping holds the goods to the pallet, not the pallet to the vehicle. The EU guidelines say plainly that straps around timber packages do not secure the load to the vehicle. For that job, see our guide to securing cargo in a container.

Checks we can do ourselves

None of these needs a laboratory, and we can do the first three in a morning.

1. Measure the strap. Use a vernier caliper for width and a micrometer for thickness, and compare both with the invoice.
2. Weigh 10 metres. IS 13960 sets a minimum weight for each PP class. For class 2B (12 × 0.5 mm) it is 3.5 kg per 1,000 m, so 10 m should weigh at least 35 g.
3. Do a float test. Push a short piece under water in a bucket and let go. PET is heavier than water and sinks, while plain PP is lighter and floats. If a strap sold as PET floats, it is not PET.
4. Look at the joints after a real trip. Check that seals have not slipped and welds have not peeled.
5. Look at the carton corners after the trip. Deep strap marks mean the load needs corner protection or less tension.

I would do the first three on every new supplier's first delivery, and again whenever a new lot looks or feels different.

Send us your load type, weight and route through our contact page, and we will suggest a strap, a joint and a tension to test first.