In Part One, you’ll find out what Thermoplastic Polyurethane (TPU) tubes are and how they’re supposed to be better. The super-short version is they’re lighter than the other air-containing options, roll almost as fast as the lightest, hold air about as as well as the longest, and the production and use is less resource-intensive and potentially more sustainable.
What to know about TPU Tubes
TL/DR—if you don’t want to know, you might not be ready for TPU.
There isn’t a lot of solid TPU insight available on most TPU purveyor sites, or on the boxes the tubes come in, and the information seems largely limited to particular products, as the advice, if you look around enough, seems to get contradictory at times. Reaching out to several TPU sellers, I got the sense that many don’t know that much about the product they’re selling as they seemed to only spout boilerplate info. A few didn’t want to talk about their tubes at all. Figuring I needed to go beyond the sellers, I tried finding an academic who might be able to opine on TPU tube issues. This, despite reaching out to several engineering departments, went nowhere. First, I had to find a TPU expert, and then someone who was familiar with pneumatic uses of the material. Perhaps because TPU has such a wide range of uses, I couldn’t find anyone.
Still, I read lots of online information and spoke to many TPU tube sellers.
If you start with websites, there seem to be a bunch of warnings about the use thereof, which should at least merit the attention of most users. Continental has a helpful list of safety tips on their TPU page. They include: don’t use with rim brakes (some of the time), use the right rim tape, don’t inflate past 0.3 bar (maybe less, maybe more) when seating the tube, make sure the valve hole isn’t too large, and the tube “must never be reused with a smaller tire!” Schwalbe has a rather long list of FAQs as well; they also don’t recommend re-using with a smaller-width tire. Other cautions include: don’t use with an electric inflator, be very careful using a CO2 inflator (or don’t use at all), use sticker-style patches (usually one to a few are included with a tube), know which tubes have removable valve cores, be careful about the valve flange/inner rim interface, don’t fill the tubes with sealant, if you do use it as an on-road tubeless repair, remove the tube when you get home and clean it, and more.
The warnings read like many a television commercial for any prescription drug: “the use of this product might result in dizziness, heart attack, or death.” Maybe there are much harder limits on TPU, maybe it’s an abundance of caution, or a fear of being sued. On that front, big, multinational companies are probably the most fearful of litigation and likely work the hardest to avoid that possibility. We should take heart in the fact that Continental and Pirelli, two huge multinationals (their bike tire businesses are probably a tiny fraction of their overall worldwide sales), are selling TPU.
The following is my best effort to address the warnings from the sellers, and concerns users might have as well as venturing into some comparison with other tubed setups. It’s hard to know if the advice given applies to all TPU tubes or just specific brands’ TPU product. So, even with all the information, I suggest deferring to warning of the specific brand you’re choosing.
Let’s address the concerns.
Don’t use with rim brakes.
This is not always the case. It probably depends on the specific tube; go with the guidance of whichever brand tube you’re using. It seems to have to do with heat generated by rim braking deforming the valve and/or the tube, and that seems to be the result of a weight issue. The overall weight of the tube has at least partially to do with tube wall thickness. The super-light TPU 700c road tubes (for 20-30mm tires), like in the 20-30g range, seem to be the ones that are specified rotor disc brake wheels only, or fixed-gear bikes being run without rim brakes. These ultralights seem to have tube walls less than 0.2mm thick. The merely light 35-50g TPU tubes almost all seem to be advertised as rim brake compatible. The heavy, 50-70g TPU tubes (still lighter than most latex and butyl tubes of the same size), often marketed as flat-resistant, seem to be all rim brake compatible. I haven’t been able to ascertain yet if the tube itself melts, or the seam fails, or the valve flange fails, or the valve stem melts, some combination thereof, or something else entirely. Butyl and latex tubes have been known to fail as well, even though it’s not common, so braking technique on rim brakes probably can make a difference—but then again, overheating is usually only the result of dragging brakes for a long time, something probably only done on long, steep descents, or carrying heavy loads, or both. And this is probably beyond the way most people ride.
Use the right rim tape.
This seems to have to do with potential sharp edges in the rim cavity, particularly by the valve. If the rim tape (don’t use cheap rubber rim strips ever) covers the valve and spoke holes, it seems like you should be fine. If you have tubeless tape, cotton tape, or a stiff plastic rim strip on your rim, you should be ok. If you have a sealed cavity inside surface rim, like those made by Mavic and Campagnolo, there might be a slight worry about the valve hole being sharp, but a strip of tubeless or packing tape over the valve hole plus punching a hole in the tape from the inside would seem to solve the problem. Silca makes a big deal about their aluminum valve stems, their flange covers, and their securing nut, suggesting that by tightening the valve nut in place reduces the possibility that the rim will cut the tube. The rationale seems solid, but since so many have run thin butyl and latex tubes without any nut, perhaps it’s merely a failsafe. Rene Herse’s TPU comes out of the same factory, and they sell TPU both with and without the securing nut.
Many TPU tubes also seem to come with a rubber washer seated at the bottom of the valve shaft. If you have a TPU tube that comes with the washer at the bottom of the valve stem, you could leave it on the tube, to go between the tube and the rim, but it’s designed to be installed on the outside, after you’ve installed the tube, to sort-of add a little friction as to minimize valve movement when installing a pump head on the valve. If you’re using a TPU tube with an entirely metal valve stem that extends to the tube, the valve hole issue is probably non-existent.
Don’t inflate past 0.3 bar when seating the tube.
That’s 4.3psi to Americans. Some others suggest up to 7psi or so is ok; one other claims the seating pressure should be more like 2psi. This has to do with how thin and stretchy (elastic) the material is. One tube purveyor suggests installing the tube at the valve before putting any air into it, to make it easier to seat the tube properly. Without a tire carcass and rim cavity holding the tube in place, the TPU tube can quickly expand past the maximum recommended tire size. The fear here is that you’ll damage the tube because nothing is constraining it. The best advice I’ve come across is that if you use your mouth to blow in enough air into the tube to give it a little shape, you’ll be fine.
Make sure the valve hole isn’t too large.
This seems to do with the limitations of the valve stem. Since many are made of plastic or TPU, or aluminum bonded to plastic or bonded to carbon-reinforced TPU, they are likely very stiff–to better hold in the valve, which is likely epoxied in place–and brittle. Variation at the valve hole and the valve stem has to do largely with manufacturing tolerances and quality control, and a loose fit could result in the valve stem moving around and potentially cracking. Some of the companies with plastic valve stems include a sticker you can place around the valve hole from the outside to reduce the hole diameter. The classic brass, or lighter aluminum, valve stem will typically bend a good bit before failing.
Here, the TPU tube merchants selling tubes with threaded aluminum valve stems and securing nuts suggest that their threaded valve stems are better because you can lock the stem in place, thus eliminating both stem and flange failures. Other sellers aren’t partial to threaded valve stems, perhaps out of necessity, perhaps out of a sincere belief that the threading makes removing a heated pump head much more difficult.
Be careful about the valve flange/inner rim interface.
This is sort of a repeat of the above. The concern seems to be that a sharp edge will cut a hole in the tube, or the flange making the tube/valve juncture. Butyl and latex tubes don’t seem to have this issue, but considering how thin the TPU tube is, the concern might have some merit. It seems that this might be a common failure point, or at least had been a common failure point. A few companies have a design where they’ve essentially mated a tubeless valve stem to a TPU tube, to prevent failures. In these cases, tubes from Rene Herse, Schwalbe, Silca, State, have a rubber gasket at the flange to protect the tube.
Don’t use an electric inflator to air up.
This, again, is a heat issue. Not only is the issue the tube itself, but the valve stem, which is often plastic or TPU and the fact that the valve itself is often epoxied into place. Most brands suggest not using an electric inflator at all, but Silca suggests that if you do so, do it in 15psi increments, waiting for the tube to cool for a minute or two in between bouts of inflation. Pirelli suggests that using an electric inflator with the hose that came supplied with it separates the heat produced by the inflator from the tube sufficiently to be safe for their Smartubes. Unless the TPU tube you buy specifies it’s ok to use with an electric inflator, the smart choice is not to do so.
Be very careful using a CO2 inflator when inflating.
This appears to largely be cold and volume issues. The cold could potentially crack the plastic or TPU valve stem, or make the tube brittle, or the blast of air, if the tube isn’t seated properly, could quickly expand the tube past its limit. While it’s easier to say not to use CO2, so many people rely on them, it’s probably impossible to write them off. Seems like the best advice offered is not to dump the entire cartridge into the tube at once—many sellers advise against blasting air into their tubes in any fashion, be it a CO2 cartridge or an air compressor. Just do quick hits, kind of like with asthma inhalers. At the same time, not every tube seller has this warning.
Use sticker-style patches (usually a one or two are included with a tube).
Most TPU tubes seem to come with a patch or two and an alcohol wipe or two. The patches generally resemble oval pieces of TPU. The first thing to know is that any TPU patch best adheres to a clean surface. Use the included alcohol wipe to clean the surface, let it dry, then apply the patch. A few sellers recommend pressing down on the patch for several seconds and then waiting a few minutes for the adhesive to cure. Some sellers say the patch is temporary while others say it’s permanent. A few sellers advertise accessory patch kits, which resemble more sticker patches. These are generally regarded as permanent, but the sellers caution that they only know the patches to work on their brand of TPU tube. There are a few YouTube videos of people allegedly permanently gluing TPU patches in place.
I’ve been trying to ascertain whether one can use a traditional sticker-style (aka “pre-glued”) patch kit with TPU tubes. Some sellers say yes. Others don’t comment.
Know which tubes have removable valve cores.
As mentioned, some valve stems are plastic, some are metal. The plastic ones all seem to have the valve core epoxied into place—you won’t be able to remove it to put on a valve extender. Even among the metal stems, some are metal all the way to the tube while others are metal bonded to plastic. Seems that the ones that are 100% metal have removable valve cores. The ones that are metal bonded to plastics sometimes have removeable cores. This component in the tube seems to be getting quite a bit of attention and it appears more and more companies are switching to aluminum stems; in general, the substitution has little to do with weight, as there might be a 2g difference at most between the materials used. In terms of valve lengths, sellers seem to have them as short as 42mm and as long as 80mm, and most sellers seem to offer at least two stem lengths for road wheels. If you have carbon fiber rims, it’s probably best to get the valve length that works with you rim so you don’t have to mess with the cores. If you have aluminum rims, the rim is probably shallow enough that any stem length will do.
Sealant and TPU tubes.
There are two parts to this. First, there is the matter of left over goo sitting on the inside of the tubeless tire that just flatted and coming into contact with the TPU tube. According to some sellers, their TPU tubes and ammonia-mixed sealants do not play well together, as the ammonia degrades the TPU. FWIW, Stans has a little ammonia, Orange Seal does not. Regardless, if you are using the TPU tube after getting a tubeless flat, you are probably best-served by removing stuck-on dried sealant when you pull the tube after the ride home and getting off all the sealant. No idea if the TPU would be destroyed by the trace ammonia in sealant getting on the tube in the time it takes to ride home.
The second part is putting sealant inside the TPU tube. Obviously, you should only do it when the valve core is removable, and using an ammonia-added sealant is probably a bad idea. Also keep in mind that latex-based sealants also has issues because TPU isn’t rubber. All the same, there are sealants designed for TPU from Rene Herse, OKO, and Eclipse, and probably some others, and some have reported Muc-Off’s sealant works here as well. However, the practical problem is that most of the sealants are designed to work by drying when exposed to air. Since the tube sits inside the tire, it is not certain that the sealant will be exposed to air, or just slowly leak into the space between the tire and tube; allegedly, the more supple the tire, the more likely it is that the hole in the tube remains aligned with the hole in the tire, thus exposing the hole to air and allowing the sealant to do its job.
The TPU tube “must never be reused with a smaller tire!”
This warning is the most paranoia-inducing of the bunch. It seems so mysterious. Does a 1mm narrower tire make a difference? What about 2mm? 3mm? Are we discussing the printed size on the sidewall, or the actual size in use? What happens when the tire is narrower?
First, keep in mind that TPU is extremely elastic. A traditional-sized TPU “road” tube supposedly can fit tires from 700c x 18mm up to 32mm according to some product information, and gravel and MTB tubes seem to have over a 20mm range that a single tube can fit. The limitation is that TPU doesn’t rebound in the way that butyl and latex tubes do. A tube in those materials might have on the box that the tube fits tires from 700c x 20-28mm; when you inflate this tube into a 28mm tire and then deflate it, it is pretty much the same width as it was before air was pushed into the tube. However, when a 700c x 18-32mm tube is installed in a 28mm tire, and then deflated and removed, it does not return to that same size.
The issues have to do with the new width of the tube. Generally, and this goes for butyl and latex tubes, one does not want to put in a too-large tube. Take that 28mm tire. If you try to install a tube that’s designed for 38-50mm tires, it probably will be pretty hard because the tube will, if one isn’t careful, will stick out beyond the tire beads, making it easier to pinch on install. So, when the tube wall thickness is much thinner than butyl, the risk of pinching the tube on installation is likely greater.
The second potential issue is what happens once the tube is encased between the tire and rim. This is what the warning is mainly about. When the tube is inflated, there might be, depending on the size of both the tube and tire, little folds in the tube where the tube is folded on itself and pressed against the tire sidewall. This will allegedly cause chafing, with the tube rubbing against itself as the tire flexes. This chafing will eventually cause a hole in the tube along the fold. Whether this would be a catastrophic failure or a slow leak seems impossible to predict.
The best advice I got on what to do is to eyeball the tube and tire. I ran a TPU tube inside a 700c x 26mm tubeless tire for a little white. It mostly sat for a few months. When I pulled it, it didn’t seem to be measurably wider than an unused version of the same sized tube. It was still around 30mm wide when flattened and without air.
Talcum powder to help install the tube.
Unlike butyl and latex, TPU seems to be less sticky and thus you don’t need to sprinkle talc on the tube or in the tire before installation. While soapy water is often advised for installing tubeless tires, I’ve never seen it for any tubed tire.
Tire mounting tricks.
I’ve come across very few. It seems that the general advice is to install one tire bead, install the tube, valve first, add just enough air to give the tube a little shape, and install the second bead, preferably without any tools. As you get toward the last little bit of bead, remove air from the tube. Arguably, because the tube is much thinner than rubber, the tube will take up less space inside the tire making the tube-style tire easier to mount in general.
Storing the tube.
Haven’t found a single explanation of why TPU tubes come rolled with the valve on the outside. It could be worth knowing. It might be as simple as it’s easier to store in boxes, or perhaps has to do with the production. No matter the reason, it’s still pretty compact. As with rubber tubes, storing with a valve cap over the valve core is a good idea. Some folks might wrap the tube in food-grade plastic wrap, but it seems to do fine on its own—according to TPU backers, the material is tougher than rubber. That written, I’d suggest putting the patch(es) and alcohol wipes in some kind of waterproof container, like a tiny Ziploc bag, so they can be used after being ignored for months or years at a time.
Recycling the TPU tube.
As mentioned in part one, a benefit of TPU is that every part of the tube can be recycled, provided the tube actually gets into a recycling program. For anyone who has access to plastic recycling, you should be able to Sadly, the closed loop systems of sellers Eclipse and Tubolito are tiny. Maybe if TPU becomes much more popular, such programs will include every bike shop. Until then…
Where we’re at:
TPU tubes are both an impressive step forward in terms of performance and sustainability, and still feel like they have lots of unsettled design and use issues. While there appear to be minor differences between the cheapest and most expensive tubes on the market, they might be qualitatively different, such that some are much safer than the others. Thing is, at this point, and without a rigorous testing protocol created and all the tubes subjected to the same tests, there’s no way to know which tubes, if any, are “better,” and whether price is an indicator of quality; the price and performance differences are definitely minor compared to the potential costs that could accompany a tube catastrophically failing.
I’m hoping that with continued use, TPU makers are gaining sufficient real-world data to refine their products so they get closer to the simplicity and reliability of butyl rubber tubes—I’m sure some will say we’re there already. It seems we’re seeing the category refined with the trend toward metal valve stems and removable valve cores.
For the leading edge types–TPU is lighter than the other air-containing options, roll almost as fast as the lightest, hold air about as as well as the longest, and the production and use is less resource-intensive and potentially more sustainable–there’s more than enough info out there to find the TPU tubes that meet your riding needs and technical know-how. For those who love the set-and-forget simplicity of rubber tubes, TPU doesn’t seem quite there yet.