Miscellaneous musings here. Tubes move relative to tires, steps or irregularities in the tire or rim bed can lead to a flat down the road, faster with thin tubes. I've repaired a couple flats for others that were caused by tire liners. The tire liners were the older thicker variety, but the standard butyl tubes had 2 lines running all the way around the tubes that corresponded to the edges of the tire liners, these eventually progressed to a hole in the tube. It was likely accelerated by low air pressure, which causes more relative movement, some used tubes show the cord pattern from the tire on them.
Continental used to put little round stickers on the inside of their tires, probably corresponding to a particular inspection. They were glued on very well so pretty difficult to remove. I was servicing a 4000S on one of my bikes and noticed that the sticker was still in place but had cracked into a number of pieces like a broken plate, still well attached to the tire. There were corresponding abraded/cracked areas on the tube at the edges of the pieces. I suspect with enough use the cracks would have progressed through the lightweight butyl tube.
Jobst Brandt, who was incredibly smart wrote "The bicycle wheel" in the 80's. He used to post his opinions on bicycle-related technology discussions way back when (there are archives somewhere). Riders would challenge him and he usually dispensed with them in short order and he was right probably about 99.85% of the time. He once discussed how tubes move relative to tires and of course they both flex in normal operation. His test example was to put a piece of card stock between tube and tire, thicker than a piece of paper but single layer, like part of a business card. It would not take that long until it was shredded.
I agree one failure mode of some TPU tubes is to develop very small holes just randomly and anywhere on the tube, including between spoke holes. I've had other TPU tubes that were still working fine after thousands of miles.
My latest experience with TPU failure is with a Cyclami 700C and I think it was partially my own fault. I had been having difficulty removing tires from tubeless ready rims and replaced the wide rim tape with narrower, which would then not occupy the areas to the sides making the rim diameter larger where the bead sits. Part of the upgrade was to make little ovals of very thin aluminum cut from soda cans and then glue them over the spoke holes. The spoke hole covers are great, but using narrow tape means there is an edge of the tape and maybe a spoke hole cover edge against the tube. The first picture is a rim with aluminum spoke hole covers and narrow tape. The second picture is the Cycalmi TPU tube and was taken after I had already patched it. Note the discolored abraded area on the tube in the middle of the shiny light reflection and also the continuous groove in the middle of the light reflection. Abraded areas circled in blue and blue line parallel to the continuous abrasion.
Assuming the inclination and energy I'd like to check the aluminum spoke covers for how well they conform to the rim curvatures in both directions so they lay as flat as possible and replace the narrow tape with something wider and probably thinner (since it's not protecting spoke holes) to eliminate the tape edges in contact with the tubes. Any changes will take a long time to show in the tubes depending on how much I'm riding, we'll see what others come up with too.
PS I think of TPU tubes like I think of higher performance tires, a bit more work and probably don't last as long, but you go faster with them.
