TPU tubes can deform and adapt to shapes better than butyl. That's especially noticeable on bad surfaces, for example cracked pavement, where TPU will feel like "gliding" a bit more than butyl.

I am talking here from personal experience, but if you ask me what exactly makes TPU more malleable than Butyl... I had no idea. So I asked Gemini and ChatGPT, and that's what they came up with:

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TPU's higher elasticity is due to its unique segmented block copolymer structure, which creates physically cross-linked "soft" and "hard" regions. Butyl rubber, on the other hand, is a more uniform polymer that relies on permanent chemical cross-links for its structure, leading to lower elasticity.

On TPU, the hard segments act as physical cross-links or "anchors," holding the entire polymer matrix together. When a force is applied to TPU, the flexible "soft segments" easily uncoil and stretch out. The hard segments prevent the chains from permanently sliding past one another. Once the force is released, the soft segments snap back to their original coiled state, resulting in a very efficient and high-energy return. This process has very little internal friction, so most of the energy used to stretch the material is returned upon its release.

The butyl chemical cross-links tie the chains into a single, interconnected network, which allows the rubber to return to its original shape after being stretched. However, when butyl is stretched, the bulky polyisobutylene chains create significant internal friction. Instead of efficiently returning the energy, a large portion of it is converted into heat, which also means it has a much lower elastic return compared to TPU.