They're both 'urethanes' - it's just a question of what the link bits between the chunky bits are:
you're right about Pebax and lower end boots being completely different.
This is interesting. Synthetic organic chemistry is outside my wheelhouse (one of my mentors once joked the only molecules he worked with were called A, B, C and D), so I'd like to understand this better. Here's what I understand thus far -- feel free to add any additions/corrections/clarifications:
I found this recent article, https://www.mdpi.com/2075-4663/1/4/78/pdf (Colonna M, Nicotra M and Moncalero M. Materials, Designs and Standards Used in Ski-Boots for Alpine Skiing. Sports 1:78–113, 2013.) (link initiates a direct download), which explains that a big source of the confusion is erroneous nomenclature by the boot producers themselves:
"TPUs can have different chemical compositions of both the urethane block and of the soft block. FTIR analysis has shown that the two most used soft blocks are polyether (e.g., poly(butyleneglycol) and poly(ethyleneglycol)) and polyester. In some cases, ski-boot producers refer in their catalogues to TPUs made with different soft blocks, simply (and erroneously) as polyethers and polyesters."
So basically, you've got the "hard" PU polymers acting as covalent cross-linkers between softer polymers, typically polyether or polyester. And it seems what's going on is that, when the softer polymer is polyester, they market the boot as made of polyurethane (since who wants a boot made from a leisure suit), and when the softer polymer is polyether, they market the boot as polyether (to distinguish it from the less expensive formulations that don't use polyether).
Interestingly, the article mentions two other materials (in addition to TPU and Pebax) from which ski boots are manufactured: polyolefin and nylon.
"According to ski-boots producers , the main classes of materials used for ski-boots are thermoplastic polyurethanes (TPU), polyolefin copolymers, polyamide (Nylon) and polyamide-polyether block copolymers (Pebax) (Figure 14)."
Edited by chemist - 10/14/15 at 4:14pm