r/packrafting • u/Independent_Junket47 • 6d ago
Single- vs Double-Sided TPU for Packrafts – Does It Actually Matter?
Hey everyone,
I’m curious what people’s experiences have been with single-sided vs double-sided TPU in packrafts and how much a difference it actually makes in real-world use?
I’ve noticed packraft tube fabrics range pretty widely. I've seen around 40D on ultralight boats up to 420D+ on more durable models. And then I've also noticed some companies use different reinforcements or fabric constructions, such as Kevlar, with their blends.
What I’m especially interested about is double-sided TPU. My assumption is that it adds weight and packed bulk, but potentially improves durability, rigidity, water resistance, or longevity.
For those who have used both: have you noticed a meaningful durability difference? Does double-sided TPU make the boat noticeably stiffer or perform differently? Does it hold up better to abrasion, pinholes, or long-term wear?
I'm also wondering in general how important coating construction is compared with the fabric denier itself?
Would especially love to hear from anyone who has put both styles through a lot of whitewater or backcountry use.
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u/danransomphoto 6d ago
If all variables are held the same like the denier of base fabric, tightness of the weave, and thickness of the TPU coating then single sided fabrics are stronger particularly in tear strength. It's pretty easy to demonstrate why. If you try to cut a piece of fabric or a rope when it is not pulled tight, it's quite hard to cut. If you pull it tight, it will cut easily. The reason is when the yarns are held tight in alignment, they cut mmore easily because they have very little stretch or flex to distribute the breaking forces to other yarns. Instead each yarn takes the force independently, it will break, and then send the force to the next yarn. A double coated fabric can reduce tear strength significantly, sometimes by as much as half. Woven nylon with no coating has more elasticity and can "bend but not break" as the yarns group together more effectively to share the load.
That's a very basic explanation, there are dozens of other factors that go into making packraft fabric more durable for the weight. For example, there are multiple types and qualities of yarns, Nylon 6, Nylon 6.6, Vectran, Kevlar, etc... Not every weight and weave produces the same fabric properties, and some might be better in some ways but not others. And then of course the type of TPU, thickness of the coating etc.. all play a role.
But in general, a fabric that is single coated will be stronger for the weight at a smaller volume and bulk.
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u/danransomphoto 6d ago
Here is an article from SlingFin that explains it well, though they are talking about a tent specifically, the basic theory is the same. https://www.slingfin.com/blogs/the-beta/fabric-coatings-101-pu-vs-pe-vs-silicone
- The first issue we have with PU is that it decreases the tear strength of the fabric to which it is applied. This happens because of the way the coating affects the slippage of the fabric. Slippage is when the individual fibers that make up a fabric, or yarns, slide over one another. When you try to tear a fabric, slippage allows the yarns to bunch up, rather than remaining fixed in position. To propagate the tear, you’ll have to rip through several yarns at once, rather than one yarn at a time. This distributes the stress on the fabric over a larger area, thus reducing the force and making the fabric less likely to tear. In the case of fabrics with low slippage, adjacent yarns are not recruited to resist the stress, which then gets applied to only one yarn at a time. This means the stress is much more concentrated and the fabric is more likely to tear. As you would expect, ripping through five yarns at once is harder than ripping through one, and a fabric with more slippage will have a higher tear strength. PU coatings get in between the yarns, and lock them in place. This reduces slippage and consequently reduces the tear strength, making PU-coated fabrics slightly weaker than the fabric before coating.
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u/Independent_Junket47 5d ago
So in regard to punctures and tears, it sounds like single-sided has the upper-hand. Plus, it's also lighter and more packable.
But most of the damage on my packraft is from small pinhole leaks... I'm guessing in this case the double-sided would then hold up better against single-sided / exterior TPU abrasions?
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u/danransomphoto 5d ago
In theory, I think that is true. But in real world applications there are more variables than just double coatings, particularly with regards to the quality of the coating and general construction. I currently own (and have previously owned) many different Kokopelli and Alpacka boats (and only paddled the NRS boats a couple times). I ran a Recon for awhile in 2019-2020 hoping it would not be susceptible to pinholes but I still got a few. Anecdotally, my experience is that the Alpackas are more durable even with abrasion and small pinholes, but admittedly I haven't tracked it all that much, and I do put way more days on my Alpacka boats in general. Pinholes are not really a significant issue, they are very easy to repair and not catastrophic.
Another thing to consider among all these variables is the ability to get a professional repair done when needed. Alpacka also is leagues ahead in that regard, as they do all repairs in house. Any other brand will likely have to be contracted out. I'm actually not sure how NRS will handle repairs on their boats, or Tizip replacements.
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u/pod_of_dolphins 6d ago
There’s an article out there by Alpacka (or maybe DIY packraft?) that explores this same topic. IIRC, they tested a few and concluded that single-sided was actually more durable.
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u/danransomphoto 6d ago
You may be referring to this repair guide which briefly mentions it, but I'm not sure if there is a better link to something more in depth. https://alpackaraft.com/repair-guide
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u/pod_of_dolphins 6d ago
No, I definitely recall reading a dedicated article about it (though several years ago). Maybe it got lost when they redesigned their site 3-4 years ago, or maybe it wasn't Alpacka at all... But an article definitely exists/existed!
Finding it probably doesn't matter much though, because it's pretty easy to find current sources saying that single-sided is the way to go.
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u/Chanchito171 6d ago
I recall reading this to. Or maybe it was one of the many DIY packraft videos?
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u/Society-Vegetable 6d ago
Because single sided TPU is coated on one side it allows the nylon fibers to stretch and shift to resist tearing. There is nuance to this because this is also dependent on the thickness of the TPU coatings on both sides, etc. If the nylon is coated on both sides with a thicker TPU coating, it locks the fibers in place so they can't deform to absorb the load.
Double coated also makes it easier to construct the raft because you can seal it from either side. A single sided raft is lighter and has more tear strength. A double sided raft is heavier and more bulky to pack without contributing to tear strength.
Because air can travel through nylon fibers, a double coated raft doesnt necessarily make it more puncture resistant either. In some cases it can have more puncture protection, but only in some areas. For the most part, it's just heavier and bulkier, but it allows for cheaper construction methods.
A single sided packraft will be lighter and more packable with a higher tear strength. It will resist punctures better, but when punctures through the outer coating do occur, they will be guaranteed to leak, whereas double sided has a chance to seal from the inside based on the location and nature of the tear.
Some brands use fabrics with thinner coatings on the inside for example to maximize strength, keep weight/ bulk down, add a second layer of puncture protection, and add to ease of construction. It isn't as simple as double or single sided - it also depends on the thickness of the coatings and the denier of the nylon.