The amount of ignorance in the last couple pages of this thread that’s stated as fact is stunning. It’s ok to not know things. It is harmful to state things you think you know but haven’t verified so matter of factly.
Some things have started to clear up lately but let’s reset the last couple pages:
TPU: The base polymer, which is often a hard plastic but can also be extruded as a film, has had widespread usage for a long long time. Powertools, laptop cases, all sorts of things. It can previously be found in shoes as a plate or shank to provide rigidity to a shoe. Just because you see the phrase “TPU” in a shoe description doesn’t make the shoe Boost-ish. An example of this is the “TPU heel cup” for the React foam. They’re referring to the hard plastic on the back of the shoe, not the foam. Same for the “TPU shank” in something like the New Balance 1500. This has very different properties before it is foamed, which is the process that BASF came up with for Boost. Characteristics of the foam include bounciness, durability, and higher density than EVA (which is why TPU foam shoes are always heavier than a similarly designed EVA shoe…the Brooks Levitate is 2 oz heavier than the similar stack height Brooks Launch). It is also more expensive than EVA due possibly in part to the difficulties in processing (speculation...could be licensing fees or greed?) (again Levitate = $150, Launch = $100). TPU also has a tendency to squish in every direction, so often these shoes need some stability features included like an EVA rim or a plastic shank (or whatever that silver sleeve Brooks puts around the Levitate foam) in order to get the springback in the direction you want. Without these features the shoe would feel much sloppier (like the Ultraboost maybe?).
EVA: Shoe workhorse, lighter, cheaper, more stable. Even shoes with these bouncier foams will probably still have some EVA components. Glad the REVlite thing got cleared up. It’s definitely EVA. It’s got the EV capitalized in the name and everything. Like all foams, you can slightly change the composition or the air content to change the durability, softness, etc. Someone said EVA is a rubber…that’s not really true, it’s not vulcanized but has some rubber like properties. If the vinyl aceteate component is on the higher side then it’s referred to as EVA rubber, but that’s a little different than the traditional definition of EVA. Furthermore, everybody’s feet and stride are different. Some people might prefer the feedback provided by TPU foam, others may prefer the more classic material or may prize lowest weight over “bounce.” People make shoes w/o TPU because customers like options and have distinct preferences (and price). EVA absolutely has adjustable “hardness”. Even within New Balance the Fresh Foam and REVlite are both EVA but they feel differently. The Clifton 4 is firmer than the Clifton 3 even though they’re both EVA.
Pebax: a name brand for a specific thermoplastic elastomer. Technically TPU is also a thermoplastic eleastomer (a square is a rectangle but a rectangle isn’t always a square) so it has a lot of similar properties (and similarly has been used as a resin in shoes previously), but Pebax is lighter (and probably less durable). Then this material is foamed like TPU to make midsoles. This is what Nike’s ZoomX foam, which is used in the Vaporfly 4%, is made from. It’s also in Reebok’s Floatride series (Run, Run Fast, Run Fast Pro). I haven’t seen confirmation that this is definitely what Boost Lite as seen in the sub2 shoe is, but I wouldn’t be surprised since the description of Boost Lite is “like boost but lighter”. I don’t think they can do that so easily with the original base polymer, so Pebax would be a logic composition. It also needs added stability or it gets sloppy, hence the carbon fiber plate in the 4%, or the EVA rim on the Floatride shoes.
Nike React is still a little bit of a mystery, but it’s definitely not TPU like Boost (if for no other reason than their claims that it’s much lighter than Boost) and it’s not Pebax because why come out with 2 similar foams with 2 different names and why claim durability. From what I found in a recent Nike patent for a new midsole material that claims many of the same properties as the React commercials and has the name of their director of materials science innovation (who was quoted in their press releases) as a named inventor: that foam is just a blend of a bunch of stuff, which could include EVA and some other rubbers. Seems like an evolution of Lunarlon not the next big thing. There’s no way to know for sure because all the listed components in the patent “could be in the range of 0-80%” or some nonsense like that, and they claim it’s different than just EVA based foams in the ads, but there’s also the option to mix EVA with other rubbers to make the EVA more durable and bouncier than EVA on it’s own. Hoka does this with RMAT, for example. Nike cleverly says React is bouncier and more durable than Lunarlon (EVA) but lighter than Boost (TPU). Which means it’s probably not lighter than Lunarlon and not bouncier or more durable than Boost. All in the marketing.
The Pegasus 35 will not be ZoomX/Pebax, but Nike will release a new shoe later this year called the Pegasus Turbo…which will have ZoomX.
Any questions?
