Carbon cycling shoes look better than traditional cycling shoes made of plastic. But the question is, do they perform better or are they only more expensive?
Well, I found a scientific study that tested the stiffness, which is a very important detail when I decide which cycling shoes to wear. Comfort and weight are also important factors, especially comfort. It is though important to remember that  shoes with the best comfort often lack stiffness.
It is very difficult, if not impossible, to achieve a high degree of stiffness and comfort at the same time.
Carbon cycling shoes are stiffer
In the study shoe stiffness measurements were collected under controlled conditions in the laboratory with a dynamic hydraulic tensile testing machine. Measurements of plantar pressure were done using a special sensor in the soles while subjects pedalled at a controlled power output.
The results from these tests showed that the carbon cycling shoes produced a significant, 18% higher peak plantar pressure than plastic cycling shoes. So carbon cycling shoes are stiffer and that is also what riders tell me when they have switched to this more expensive foot wear.
One extra bonus due to this additional stiffness is that it is possible to make carbon cycling shoes even lighter and still have a high level of performance.
Though, if you have problem with metatarsalgia or ischemia, it is probably better for you to choose a more flexible cycling shoe.
Reference:
Foot Ankle Int. 2003 Oct;24(10):784-8.
The effects of cycling shoe stiffness on forefoot pressure.
Jarboe NE, Quesada PM.