Vaporfly Dissection – Brett Sanborn

December 7, 2018

The talk about the Nike Vaporfly 4% shoe is constantly about the carbon plate embedded in the midsole. But how much do we really know about the carbon plate? Luckily, a friend had a pair of Vaporfly shoes that were no longer useable. I took the opportunity (and a bread knife) and proceeded to dissect the Vaporfly to see what was inside.

Aside from this image that I found in an Alex Hutchinson article on RunnersWorld, I couldn’t find too much information on the carbon plate:

This image gives us the general shape of the plate but doesn’t tell us anything else. I’d like to know things like the plate thickness profile and possible manufacturing methods.  

Starting with the Vaporfly shoe, I cut away the bottom using a bread knife:

Here, you can start to see the plate peeking out from the middle of the foam:

The plate is closer to the bottom of the contour of the shoe, rather than being perfectly in the middle of the sole:

 After the upper is cut away, you can see the top of the plate embedded in the foam:

The foam is strongly adhered to the carbon plate. A lot of hacking was required to remove the foam layers.

Now you can see the overall shape of the plate that matches the one seen in the RunnersWorld article: 

At this point, the foam was very tough to remove. I hoped that I would be able to melt the foam with a solvent, but it turned out that the foam was quite chemical resistant. I tried acetone, methyl ethyl ketone (MEK), naptha, and a product called “goo-off” which smelled pretty noxious, but nothing melted the foam. I had to resort to mechanical means to remove the foam:

After grinding away for a while, I was finally able to get down to the carbon layer itself, with only a small amount of residual foam and adhesive:

Overall, the shape of the Vaporfly carbon plate looks like the image that Nike put out there. This gives a direct verification of the plate shape and size. It is also worth noting that the plate covers the entire ball of the foot. Nike also did not keep as much carbon near the mid or rear of the shoe, indicating that the area around the ball of the foot is more critical.

The plate feels more flexible in the transverse direction compared to the longitudinal direction. This indicates that the plate was most likely made using unidirectional pre-preg carbon fiber. “Pre-preg” or pre-impregnated fiber is manufactured with epoxy resin present. The fibers are oriented in one direction while the epoxy matrix holds the material together. The plates were most likely vacuum-bagged and or autoclaved to press the fibers together as much as possible to minimize void and increase the stiffness. The carbon can either be pre-cut and then heated under vacuum in the final shape to cure, or cured first and then cut out. The use of pre-preg has the benefit of achieving close to the lowest weight possible for the finished plate, compared wet-layup methods where removing the as much epoxy from the matrix is critical. Carbon pre-preg material would also give the best repeatability for large-scale manufacturing.  

The Vaporfly plate had an average thickness of about 1 mm, or about .039 inches.  The overall weight of the plate was approximately 25 g for a men’s size 11. This is about 0.88 oz and contributes about 11% to the overall shoe weight of 7.76 oz.

In terms of improving other shoes, it may not be enough to simply add a 25 g, 1 mm thick plate to an existing ~6 oz shoe. The fact that the plate is offset from the bottom of the foot may contribute to the spring action that it gives. The ZoomX foam, shoe shape, or some other factors may also play a role.