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Stroke & Stern

PVC, polyurethane, Hypalon and drop-stitch, explained

Half the words on an inflatable spec sheet are trademarks. Here is what the underlying materials and constructions actually are.

By Scooter M. · Published September 2, 2026 · Last updated September 2, 2026

Rolls of technical fabric stacked together

Read four inflatable spec sheets and you will meet Polykrylar, Duratex, ESL, FusionTech, MSL, AerGlide-Lite and "military-grade PVC". Every one of those is a trademark, none of them is measured against a common standard, and underneath them there are only about four things going on.

The short version
  • PVC is the default: cheap, tough, weldable, heavy, and it does not love UV.
  • Polyurethane is much lighter for its strength and less abrasion-tolerant. It is how a 4 lb kayak exists.
  • Hypalon is the long-life expedition material. Nothing in our registry uses it.
  • Drop-stitch is a construction, not a material -- it is what makes a flat panel possible.

PVC

Polyvinyl chloride over a woven fabric scrim, and the default for almost everything in this category. It is cheap, genuinely tough, resists abrasion well, and can be heat-welded rather than glued, which makes seams fast to produce and reliable.

Its weaknesses are weight and UV. PVC is heavy for its strength and it becomes brittle with long sun exposure, which is the mechanism behind most old-inflatable failures.

In our registry: the Sea Eagle SE370's 38 mil Polykrylar (which Sea Eagle itself identifies as K80 PVC), the Intex Excursion Pro K2's three-ply PVC laminate over a polyester core, Sevylor's 21-gauge PVC, and the drop-stitch skins on essentially every paddle board here.

What "three-ply" means and why it matters

A PVC layer, a woven polyester scrim, another PVC layer. The scrim is the important part: it is what stops a puncture propagating into a tear. A single layer of PVC that gets nicked can rip along the cut; a scrim-reinforced one stops at the hole.

Polyurethane

Considerably lighter than PVC for the same strength, and the reason the Advanced Elements PackLite is 4 lb rather than 15. Advanced Elements describes it as fabric-reinforced polyurethane over a PVC-free polyester ripstop, which is the same scrim principle applied to a lighter coating.

The trade is that a thinner, lighter skin is a less abrasion-tolerant one. That is not a defect; it is the whole design. It is also why we tell people not to fish from it.

Hypalon

Chlorosulfonated polyethylene, the traditional choice for commercial RIBs, expedition rafts and anything that lives outside. Outstanding UV and chemical resistance and a very long service life.

It is heavier than PVC, more expensive, and it cannot be heat-welded -- seams have to be glued, which is slower and more skilled work. Nothing in our registry uses it, and that is a fair reflection of where the recreational market has landed: for a boat used a few dozen times a year and stored indoors, PVC's weaknesses barely surface.

Drop-stitch: the construction that makes boards possible

This is the one worth understanding properly, because it explains why a paddle board runs at 15 psi and a kayak runs at 2.

Take two sheets of PVC-coated fabric and run thousands of threads between them, all exactly the same length. Inflate the space between. The threads go into tension and stop the sheets bowing apart, so instead of becoming a pillow, the panel stays flat and becomes rigid.

The threads only work under tension, and tension needs pressure -- which is why drop-stitch panels need 15 psi where a round tube is happy at 2. It is also why an under-inflated board sags in the middle: below a certain pressure the threads slacken and the panel goes back to behaving like fabric. The pressure chart has every published target.

Single-layer, dual-layer and fusion

Budget boards typically glue a single outer layer over the drop-stitch core. Better ones bond two layers, which is stiffer and heavier. "Fusion" and "laminated" constructions -- NIXY's FusionTech, Atoll's MSL Fusion, Bluefin's ESL -- are machine-laminated processes that get the strength of a dual layer with less glue and less weight.

These are real engineering differences and they are also proprietary names with no shared standard behind them. You cannot compare FusionTech against MSL Fusion from the spec sheets, and any site that ranks them against each other is inventing the comparison.

What to actually look for

A thickness or a denier figure, if anyone will give you one. Sea Eagle's 38 mil is the only such number in our whole registry.

Failing that: a warranty term, which is a manufacturer putting money behind the material rather than an adjective. Bluefin publishes five years and NIXY three. Everybody else in our registry publishes nothing at all, and that is its own kind of specification.

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Questions people actually ask

Is drop-stitch a material?
No, and this is the most common confusion in the category. Drop-stitch is a construction: thousands of threads run between two fabric skins, holding them a fixed distance apart so the panel inflates flat instead of round. The skins themselves are usually PVC. Every paddle board in our registry is drop-stitch, and so is the floor of the Aquaglide Chelan 120.
Is Hypalon better than PVC?
For UV and chemical resistance and long-term life, yes -- it is the traditional choice for commercial and expedition inflatables. It is also heavier, more expensive, and glued rather than welded, which makes manufacturing costlier. Nothing in our registry uses it, which tells you where the recreational market has settled.
What is 'military-grade PVC'?
A marketing phrase with no standard behind it. GILI uses it for the Air 10'6 and several other brands use similar language. It is not a specification and it is not comparable between brands. When you see it, look for a thickness or a denier figure instead -- and in this registry you will usually not find one.
Why is polyurethane used on the lightest boats?
Because it is dramatically lighter than PVC for a given strength. The Advanced Elements PackLite's fabric-reinforced polyurethane is how a 4 lb kayak exists at all. The trade is abrasion tolerance -- it is a thinner, more delicate skin, which is why we recommend that boat for carrying a long way and not for fishing.

Sources

Every specification on this page was read from one of these, on the date shown. Specs change between model years, so the date matters as much as the link.