Epoxies are polymerizable thermosetting resins and are  available in a variety of viscosities from liquid to solid.  There are many different types of epoxy, and the technician  should use the maintenance manual to select the correct type  for a specific repair. Epoxies are used widely in resins for  prepreg materials and structural adhesives. The advantages of  epoxies are high strength and modulus, low levels of volatiles,  excellent adhesion, low shrinkage, good chemical resistance,  and ease of processing. Their major disadvantages are  brittleness and the reduction of properties in the presence of  moisture. The processing or curing of epoxies is slower than  polyester resins. Processing techniques include autoclave  molding, filament winding, press molding, vacuum bag  molding, resin transfer molding, and pultrusion. Curing  temperatures vary from room temperature to approximately  350 °F (180 °C). The most common cure temperatures range  between 250° and 350 °F (120–180 °C).  [Figure 7-10] ultimate properties of a composite material. Thermosetting  resins are the most diverse and widely used of all man-made  materials. They are easily poured or formed into any shape,  are compatible with most other materials, and cure readily  (by heat or catalyst) into an insoluble solid. Thermosetting  resins are also excellent adhesives and bonding agents. Polyimide resins excel in high-temperature environments  where their thermal resistance, oxidative stability, low  coefficient of thermal expansion, and solvent resistance  benefit the design. Their primary uses are circuit boards  and hot engine and airframe structures. A polyimide may be  either a thermoset resin or a thermoplastic. Polyimides require  high cure temperatures, usually in excess of 550 °F (290 °C).  Consequently, normal epoxy composite bagging materials are  not usable, and steel tooling becomes a necessity. Polyimide  bagging and release films, such as Kapton$^{®}$ are used. It is  extremely important that Upilex$^{®}$ replace the lower cost  nylon bagging and polytetrafluoroethylene (PTFE) release  films common to epoxy composite processing. Fiberglass  fabrics must be used for bleeder and breather materials  Polyester resins are relatively inexpensive, fast processing  resins used generally for low cost applications. Low smoke  producing polyester resins are used for interior parts of  the aircraft. Fiber-reinforced polyesters can be processed  by many methods. Common processing methods include  matched metal molding, wet layup, press (vacuum bag)  molding, injection molding, filament winding, pultrusion,  and autoclaving. The appearance, handling properties, and curing characteristics  of vinyl ester resins are the same as those of conventional  polyester resins. However, the corrosion resistance and  mechanical properties of vinyl ester composites are much  improved over standard polyester resin composites. Phenol-formaldehyde resins were first produced commercially  in the early 1900s for use in the commercial market. Urea- formaldehyde and melamine-formaldehyde appeared in  the 1920–1930s as a less expensive alternative for lower  temperature use. Phenolic resins are used for interior  components because of their low smoke and flammability  characteristics. Figure 7-10.  Two-part wet layup epoxy resin system with pump  dispenser.  Phenolic Resin Vinyl Ester Resin Polyester Resins Polyimides Figure 7-9.  Aluminum mesh lightning protection material. Epoxy 7-7