Inflatable Kayak Fabrics

See also
Hull forms and rigidity
Tubeless Vs Bladders
Glues and repairs
A ‘PVC vs rubber’ article from 2011 by The Boat People
PVC vs PU vs synthetic rubber: slightly biased. Skip to: 2. Characteristics of the Material

Cheap IKs are made from a film of heat-welded vinyl, like a slackraft (or a bin bag, but thicker). They’ll float, but run 1–1.5psi to avoid bursting and so sag horribly, track poorly. Some might also say they look a bit crap and are responsible for the ‘pool toy’ image which IKs suffer. These boats are OK for messing about near the water’s edge, but many end up in the trash or back on eBay after being used just a couple of times.

A 12-year-old Grabner H 2 showing the polyester core
fabric (that boat has since been renovated).

Broadly speaking (I say that a lot for legal reasons), quality inflatable kayaks use material comprised of a densely woven fabric core coated in either ‘synthetic rubber‘ or ‘PVC, as the image left demonstrates.
The almost ballistic core adds strength and all but eliminates elasticity which means pressures can be higher, greatly improving performance, unlike a pure vinyl IK which just keeps expanding and expanding like the universe.

Synthetic rubber (‘Hypalon’)
These use a nylon or polyester woven core. Nylon is stretchier which is good for resisting punctures but less good for rigidity. Either are coated with natural rubber or neoprene on unseen inner surfaces. The exterior surface is then coated with a durable synthetic rubber coating, the best known being DuPont’s hypalon. Hypalon® is the coating on the fabric, not the fabric itself, but most use the word to generically describe rubber boats.
As folding boat makers, Pakboat put it on their website: ‘The abrasion resistance [and waterproofing] is in the coating, and the tear strength and tensile strength are in the woven fabric.’

nylonpoly

Examples include the original Hypalon, invented after WWII by DuPont and which could be said to have helped kick-start the inflatable boat and RIB boom. No longer made or trademarked. the word ‘hypalon’ is still bandied about as it sounds cool but actually refers to the coating, not the finished material.

Hypalon fabric is composed of three plies all bonded together:
• an inner coating of neoprene or natural rubber makes it airtight and easy to glue
• a fabric core of polyester or nylon weave resists stretching and tearing
• the durable hypalon outer costing resists UV and chemicals better than just about anything.

A near-identical product is now supplied, among others, by Pennel in France under the ‘Orca‘ brand (above left) as used on US-made NRS IKs. Gumotex’s various in-house Nitrilons (below) are similar, as is Dow’s ‘Nordel‘ EPDM, as bought in by Grabner (above right) as well as some folding kayak makers and raft manufacturers.

Gumotex vulcanising autoclave

Gumotex inflatables are glued together by hand. Some not very illuminating photos here with no gluing to be seen. Gumotex limit the safe operating pressure of most of theor boats to a modest 0.2 bar (2.9psi), still more than many well known IKs.
A couple of round tube Gumotex IKs like the K whitewater series and the Seawave sea kayak run 0.25 bar (3.6 psi). Somewhere along the line the fabric is vulcanised, probably in the chemically bonding the coating sense, rather than assembly

fab-frab

Austrian Grabner make a big deal of their EPDM boats being vulcanised, but again this is related to preparing or curing the fabric, not assembling the sections of EPDM. Vulcanising is a chemical reaction which either molecularly bonds rubber to itself (as in the autoclave drum, above left) or makes a rubber product such as a tyre more durable. One problem with synthetic rubbers is they cannot be ‘machine welded’ – they need to be laboriously glued by hand.
However they do it, Grabners manage to run high pressures for a traditional round-tube IK and amazingly, don’t feature pressure release valves (PRVs), even in the I-beam floor.That shows confidence in manufacturer.

PVC
These days most IKs are made from cheaper PVC-coated fabrics. Remember, with PVC this is not the plastic film of a novelty pool pizza, but PVC bonded onto a nylon or polyester fabric core and, just like Hypalon rubber, makes a flexible, durable and airtight coating that’s less pliant (hard to roll up) but also stiffer (good on the water.

featherf

The great thing with PVC is that it can be easily and quickly heat welded. No gluing required. Heat welding PVC is so easy and effective you can even do it yourself with roller and a heat gun. The process was invented in 1948 in France by SEVY, the company that went on to become Sevylor. They produced an inflatable PVC bath that became a hit in post-war austerity France and since that day Sevylor has never looked back. Though some paddlers have.

In environmental terms, PVC has become a bit of a dirty word which is why Gumotex and Grabner make such a song and dance about their IKs not being made from PVC. Apparently toxic chemicals like DEHP (below) leach out of the material and it degrades internally over time. This outgassing is what gives PVC it’s distinctive plasticy smell.

It’s staggering to note the lengths that boat makers like Ally Canoe, Pakboat, Sea Eagle and even Aire will go to not to mention ‘PVC‘ by name. They will just describe hull material as ‘1100 Decitex Reinforced’ or ‘Base Fabric Denier 650/1000’, but meantime the bladder cells (see below) are proudly identified as urethane. But PVC it is and so all US vendors must post a warning above if they dare sell PVC products in the Sunshine State. Will using a PVC IK make you ill? It’s extremely unlikely but Californian environmental law – the strictest in the US – insists on the warning.

pvcwarning

So, Rubber or Plastic?
Synthetic rubbers like Nitrilon and EPDM are tough, durable and more expensive than PVC, metre for metre. On a same-sized boat, they’re also more pliant and will roll up much more compactly than PVC (left, a 4-metre Nitrilon Sunny). Importantly, this means creases and folds cannot develop into cracks and leaks, as I’ve found on PVC boats.

Synthetic rubbers also have very good resistance to UV and solvents, are said to be heavier than comparable PVC and come is fewer colour options. Rubber used to be the classic material for river-running rafts (above, Lees Ferry, Grand Canyon) that put in years and years of reliable service. But being a form of rubber, not plastic, it cannot be heat welded in a machine like PVC; it must be labouriously glued which, when done well, increases costs. It can also be heat vulcanised which might be regarded as a form of heat welding.

vanguard
Table lifted from: http://www.vanguardinflatables.com
Bear in mind, like the link at the top of the page, it may be a little biased to validate their choices of material.
303

This is why Grabners, NRS MaverIKs and proper river running rafts all cost so much. They’ll easily outlive your pet and might be considered over-the-top for a recreational IK’ing. 
Inexpensive recreational IKs are made from PVC film or PVC-coated fabrics – usually shells containing separate air bladders. It’s likely that not all PVC is nasty, toxic crap, just as not all alloy bicycle frames are the same quality. In the hands of a careful owner – as opposed to the hard use from a river-running outfit – with proper care and maintenance involving anti-UV 303 protectorant (right), thoughtful handling, drying and storage, a PVC IK should still last for years provided the initial material and quality of manufacture is high. And while suitably chunky PVC IKs like my old Incept K40 are hard to fold, that stiffness translates to a more rigid and therefore faster boat on the water without needing to resort to high pressures. This was apparent when I first tried a K40 after running a Nitrilon rubber Sunny for years.


Fabrication: ‘bladder’ vs ‘tubeless’
An IK’s hull can be a casing or ‘envelope’ with three chambers (two sides and the floor) made of PVC, woven nylon or both into which are fitted or zipped light, removable sponsons or air bladders, made either from stiffer, ‘brittle’ vinyl, more durable and flexible urethane, or even PU-coated nylon. Examples include Aire, Aquaglide and Advanced Elements.

Ironically, the very cheapest Sevylors (as above) as well as the most expensive Grabners are both tubeless IKs. The difference is the Sevy is heat-welded vinyl, like an inflatable globe or a bin bag. Keep pumping and it will pop. While a Grabner is made from synthetic rubber bonded to an unstretchable polyester fabric core (EDPM) which is glued and/or vulcanised together. It will last 20 years; I’ve seen cheap vinyl-tubeless slackrafts ruined in less than 20 metres.
bladdio

Pictured right: vinyl and urethane may all be just ‘plastics’, but might be compared to Platypus water bladders (vinyl, stiff, slippery) and the blue Camelbak (softer and rubbery). That is why in bladder boats like Aires, PVC is good for the shell and urethane makes an ideal, slightly stretchy bladder. Cheaper Aire Tributary IKs us vinyl. Compare that to the Gumotex, Grabner, Sea Eagle, NRS and Incept style of fabrication which involves the perfect gluing of the hull sections keeps the air in.

I notice my ‘tubeless’ analogy was adopted by Innova, the US Gumotex importers, except that they try to make out that ‘tubeless’ is superior. It certainly is for automotive tyre use, but with IKs it’s more down to manufacturing ease and therefore, costs. PVC (welded is best, like Incept or some Aires, not glued like Advanced Elements or sewn like Tributary) is stiffer once pumped up, less durable, doesn’t abrade so well on grit (out of the water), but is less expensive than synthetic rubbers, quicker to weld or sew, and is slipperier in the water, so giving better response when combined with its superior stiffness. The difference between the ‘tubeless’ or ‘tubed’ construction style is merely down to the cost of manufacture and materials.

The floor and two side bladders or inner tubes which slip into the woven nylon green hull shell or envelope.

Boats with air bladders slip into woven nylon or PVC shells. Sealing this hull shell isn’t critical; they can be heat welded, sewn, glued, or just zipped together and the bladders inside are pumped up until the hull takes form.
But durability and the material of the hull shell is a factor. Heat welding PVC is best, certainly compared to vulnerable stitching. The green shell of the boat above was ripped on its second outing (possibly over inflated then got hot in the sun). I also read that on cheaper IKs, sponsons can get twisted in the sleeves during unrolling and inflation which can get to be a faff. That, and much quicker and easier drying/cleaning is why I prefer tubeless IKs. If your boat is in and out of your car boot or motorhome hatch, tubeless is the way to go. If you’re more into multi-day trips and have time and space to dry it, a bladder boat has no disadvantages.

Tubeless Gumotex boat, simply splay it out, brush out any dirt and wipe off the moisture. On a warm day it takes 5 minutes.

The problem with bladder boats is that although the best-made ones perform well, it’s normal for some water to seep inside the hull shell to the pumped-up bladders. Result: the boat takes ages to dry properly. This may not matter in Acapulco, but it sure does in Scotland or Scandinavia or Seattle. Coming back tired from a long paddle and then packing a wet boat is as undesirable as packing a wet anything, not least if it’s seawater. Mildew may develop, grit may get in and who knows, something may rot and shorten the life of your boat (although Aire says that a little water in the chambers does no harm, even long-term). When I come back from a sea paddle I always hose my IK down.

Dropstitch fabric is discussed in the next article.

sempauto - 1

Conclusion
Tubeless construction seems to be the traditional or ‘European’ method and, if well made will last for decades as rafters know well (left, a hypalon Semperit from the 80s). Our Nitrilon Gumotex Solar looked as good as new when I sold it some nine years on, and had my Incept K40 been made from the same material I’d have probably kept it. Bladdered IKs are about cost-saving.

bladderboy

I like the simplicity of tubeless IKs: a tough outer shell that is well sealed. There is no cheap way of doing it and so any tubeless IK like a Gumotex, Sea Eagle (PVC) or Grabner ought to be a well-made IK.
In my experience in the US, IK rental outfitters tend to use tubeless Hypalon IKs like NRS, even if most recreational IKs sold are bladdered. Tubeless will cost more but they’ll last much longer, especially if made from synthetic rubber.

Part 2: Hull forms, Rigidity and drop stitch

gumk44
Two tubeless IKs: a Nitrilon Gumotex and a PVC/PU Incept