Historically, rigid metal plates were used to stiffen up the shoes to make them more rigid when there was a clinical condition of the foot that making the forefoot more rigid would benefit from this (eg hallux rigidus). The use of steel plates or strips was the most practical then and was adequate to do the job, but working with steel or other metals was not the easiest.
In the 1960’s the Union Carbide Corporation in the United States started doing research into high-strength materials and produced the first carbon fiber sheet material. In the 1980’s the carbon fiber sheets became more commercially viable due to improvements in manufacturing technology and the carbon fiber sheets began to be used in a wide range of industries such as aerospace, automotive and sports equipment.
The sheets are typically made by layering sheets of carbon fiber fabric or a prepreg material (carbon fiber impregnated with resin) together, and then compressing and curing the layers to form a rigid sheet like structure. The rigid carbon fibre sheet material is then cut out, typically using a water jet cutter to make insoles or inserts to use in footwear to make them more rigid. The material was very rigid for a relatively small thickness of the material.
It is not possible to now get the steel or metal plate inserts commercially to do this any more.