Strapping applies tension through a load rather than around it, which is why it holds heavy items that film cannot. Polypropylene suits light bundling, PET replaces steel on most palletised loads, and steel remains for extreme weight and sharp edges.
What strapping does that film does not
Stretch film contains a load by wrapping it. Strapping applies tension along a line, pulling the load down onto the pallet or holding a bundle together along its length. The difference matters as soon as weight is involved, because film relies on friction and strapping does not.
They are frequently used together rather than as alternatives: strapping takes the structural load, film contains the smaller items and keeps weather and dust off. On a heavy pallet, either on its own is doing half a job - see Pallet Wrap and Stretch Film: A Buyer's Guide for the film side, and industrial packaging for the full range of load protection.
The three strap materials
| Material | Strength | Best for | Watch out for |
|---|---|---|---|
| Polypropylene (PP) | Light to moderate | Bundling, light cartons, closing cases | Stretches and relaxes over time |
| Polyester (PET) | High, with good retained tension | Most palletised loads; replaces steel | Needs correct tensioning equipment |
| Steel | Highest | Extreme weight, sharp edges, high heat | Rusts, cuts, hazardous to remove |
| Woven cord | Moderate to high | Awkward loads, no sharp edges | Bulkier, more expensive |
| Paper | Light | Recyclable single-material bundling | Low strength, moisture sensitive |
Strapping materials compared.
PET is the one that has changed most operations. It retains tension far better than polypropylene as a load settles, does not rust, is safer to cut, and on most palletised work does everything steel was used for.
Retained tension, and why loads come loose
Applying tension is easy; keeping it is the engineering problem. Loads settle in transit - cartons compress, product shifts slightly - and a strap that cannot take up that slack goes slack itself. Polypropylene relaxes noticeably; polyester holds far more of its initial tension.
That is why a load can leave the bench strapped correctly and arrive with loose straps. The usual diagnosis is that the strapping failed; the actual cause is a material that was never going to retain tension through the settling that was always going to happen.
Sealing and application
- Friction weld - the standard for PET and PP with powered tools; no consumable seal needed.
- Metal seals and crimps - used with steel and heavier PP; requires a sealer.
- Heat seal - common on lighter automated lines.
- Manual tensioner and sealer - workable at low volume; tension varies with the operator.
- Battery tools - consistent tension, far faster, and the usual answer once volume justifies them.
Inconsistent tension from hand tools is a common hidden problem: the same load strapped by two people can behave completely differently in transit.
Protecting the load from the strap
A tensioned strap concentrates force exactly where it crosses an edge, which is where cartons are weakest. On anything with crushable corners the strap will cut in, and the damage shows as a crushed edge rather than as a strapping failure.
Edge protectors under the strap solve it, and they are the same component that handles stretch film cutting in - see Corner Boards, Edge Protection and Pallet Stability. On heavy palletised work the combination of corner boards, strapping and film is a complete specification where any one alone is not.
Choosing for a specific load
- Light bundling, no sharp edges - polypropylene, hand or machine applied.
- Palletised cartons, moderate to heavy - PET with powered tools and corner protection.
- Very heavy, sharp-edged or hot - steel, with the handling risk managed.
- Single-material recyclable pack - paper strapping on light loads only, see sustainable packaging.
- Irregular or delicate loads - woven cord, which spreads force more than a flat strap.
Getting the tension right
Tension is the variable that decides whether strapping works, and it is the one most often left to chance. Too little and the load moves; too much and the strap crushes the cartons it is supposed to be holding.
| Symptom | Likely cause |
|---|---|
| Strap loose on arrival | Material relaxation - usually PP where PET was needed |
| Cartons crushed under the strap | Over-tension, or no edge protection |
| Strap snapped in transit | Under-specified width or grade for the load |
| Load shifted but strap intact | Strap not tied to the pallet, only around the load |
| Inconsistent results | Hand tensioning - varies with the operator |
| Seal failed, strap intact | Wrong seal method or a worn sealing tool |
Tension problems and what causes them.
The fourth row is the one people miss. A strap around a load holds the load together; a strap through or under the pallet ties the load to the pallet. Those are different jobs and a load that shifted off its pallet with the straps still intact was only ever doing the first - the same distinction as base-locking in Pallet Wrap and Stretch Film: A Buyer's Guide.
The short version
- Strapping tensions through a load; film contains around it. Heavy work needs both.
- PET has replaced steel for most palletised loads - safer, no rust, good retained tension.
- Polypropylene relaxes as a load settles, which is why straps arrive loose.
- Hand tools give inconsistent tension; powered tools fix that.
- Edge protection under the strap prevents it cutting into the corners.
Frequently asked questions
What is the difference between PP and PET strapping?
Polypropylene is lighter, cheaper and relaxes over time, which suits bundling and light cartons. Polyester holds far more of its tension as a load settles, which is what makes it suitable for palletised work.
Has PET replaced steel strapping?
For most palletised loads, yes - it is safer to handle and cut, does not rust, and retains tension well. Steel remains where weight is extreme, edges are sharp, or temperatures are high.
Why do our straps arrive loose?
Usually because the material relaxes as the load settles in transit. Polypropylene does this noticeably; switching to polyester retains far more of the applied tension.
Do we need a powered strapping tool?
Once volume is meaningful, yes. Hand tensioners vary with the operator, and inconsistent tension produces loads that behave unpredictably in transit.
Will strapping damage our cartons?
It will cut into crushable edges without protection. Edge protectors under the strap prevent it, and they are the same component that stops film cutting in.