One Dutch reviewer (Aerothan) claims that the PU material has a tendency to close punctures somewhat, so the punctured tube deflates slower than butyl. This may be an advantage on the road (gives you a bit more time to find a decent spot for flat repair), but he also had a hard(er) time locating the puncture because of that. Not ideal for road side repairs (I had 13 flats last summer ). I'm also curious about the durability of the patches on the TPU. I've had bad experiences with self-adhesive patches for butyl and don't use these anymore.