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You are choosing a material to carry a load, full stop. “Strongest” sounds like a single figure, but genuine straps fail or survive based on more than an ultimate break test. How the webbing behaves on the way to failure matters: stretch under impact, loss of capacity when wet, and drift under a steady pull. The goal here is to focus only on strength and explain why the answer shifts as the load and conditions change, so you can spec a webbing strap that is strong in the way you actually need.
In dry, room-temperature tests on comparable constructions, nylon and polyester sit in the high-strength class, with polypropylene well behind. The gap between nylon and polyester is small enough that construction and yarn grade can swap the order on a given test. Polypropylene does not approach the same peak loads for a comparable size. That is the clean baseline. What moves the ranking is moisture, load type, and the duration the strap remains loaded.
If the strap gets soaked or is exposed to water, its strength does not stay the same. Nylon webbing absorbs moisture, which softens the polymer and trims peak capacity until it dries again. Polyester barely absorbs water, so its wet break strength tracks closely to its dry result. Polypropylene also sheds water, though its absolute break number is lower to begin with. If “strongest in the rain” is the job, polyester often becomes the practical winner because it keeps what it has when wet.
A strap that stretches can be stronger in practice because it keeps a sudden spike from ever reaching the break point. Nylon webbing stretches more than polyester and polypropylene, which lets it absorb impact and reduce peak stress. Polyester stretches less, which is helpful when you need a fixed length and stable tension under a steady pull. Polypropylene has some give, but not enough muscle to be the shock choice.
Two straps with similar lab break numbers will behave differently in the field. The one that stretches under a jolt will often survive the event that snaps the stiffer one, even though their ultimate strength looks alike on paper.
Hold a strap under load for hours or weeks, and you are no longer judging day-one break strength. You are dealing with creep, the slow, permanent lengthening that steals adequate capacity. Polypropylene shows the most creep, nylon is moderate, and high-tenacity polyester is the most resistant of the three. If your application keeps tension on the strap, plan for this or choose the material that resists it.
Pick the scenario that matches how your strap actually carries force. Some bullets go deeper where decisions tend to go wrong.
When you come to National Webbing with a strength question, we match the test to your use instead of handing you a catalog number. For wet service, we run the same construction dry and then, after water conditioning, send both curves so you can see the drop and make an informed decision. For shock-sensitive builds, we characterize the stress–strain shape so you can see how nylon’s elongation lowers peak force. For long-held loads, we add a simple creep exposure that mirrors your duty cycle, then confirm retained break strength. The deliverable is small and practical: curves, break loads, and a one-page acceptance you can paste into a PO.
The thesis stays simple. Nylon and polyester live in the strength class; polypropylene does not, and the right choice between nylon and polyester depends on how the strap carries force. Water pushes the decision toward polyester because it keeps its capacity when soaked. Shock moves you toward nylon webbing because it stretches and protects against peaks. Long, steady pulls favor polyester because it creeps less and keeps usable strength longer.
