There are many products that utilize the concept of prepreg among which is the following. Motorsport Space travel Sports equipment Sailing Orthopedic technology in orthotics as well as in prosthetics In electrical engineering as an "intermediate layer" in multilayer circuit boards and as insulating material for electrical machines and transformers Rotor blades in wind turbines Applicable fiber types There are many fiber types that can be excellent candidates for the preparation of preimpregnated fibers. The most common fibers among these candidates are the following fibers. Glass fibers Glass cloth Basalt fibers Carbon fibers Aramid fibers Matrix One distinguishes the matrix systems according to their hardening temperature and the type of resin. The curing temperature greatly influences the glass transition temperature and thus the operating temperature. Military aircraft mainly use 180 ° C systems Composition The prepreg matrix consists of a mixture of resin and hardener, in some cases an accelerator. Freezing at -20 ° C prevents the resin from reacting with the hardener. If the cold chain is interrupted, the reaction starts and the prepreg becomes unusable. There are also high-temperature prepregs which can be stored for a certain time at room temperature. These prepregs can then be cured only in an autoclave at elevated temperature. Resin types It is mainly used resins based on epoxy resin. Vinyl ester-based prepregs are also available. Since vinyl ester resins must be pre-accelerated with amine accelerator or cobalt, their processing time at room temperature is shorter than with epoxy-based prepregs. Catalysts (also called hardeners) include peroxides such as methyl ethyl ketone peroxide (MEKP), acetyl acetone peroxide (AAP) or cyclohexanone peroxide (CHP). Vinyl ester resin is used under high impact stress. Resin properties The properties of the resin and fiber constituents influence the evolution of VBO (vacuum-bag-only) prepreg microstructures during cure. Generally, however, fiber properties and fiber bed architectures are standardized, whereas matrix properties drive both prepreg and process development. The dependence of microstructural evolution on resin properties, therefore, is critical to understand, and has been investigated by numerous authors. The presence of dry prepreg areas may suggest a need for low viscosity resins. However, Ridgard explains that VBO prepreg systems are designed to remain relatively viscous in the early stages of cure to impede infiltration and allow sufficient dry areas to persist for air evacuation to occur. Because the room temperature vacuum holds used to evacuate air from VBO systems are sometimes measured