When building very large objects, such as an airplane wing, it no longer becomes possible to hand lay epoxy. In these cases pre-impregnated carbon fabrics are used (prepregs). Since the epoxy resin & hardener must be combined in prepreg fabrics, typically a temperature threshold must be met in order for the resin to cure (ex. 300 Degrees F).
II. Advantages of Prepregs
The lack of need to mix the epoxy and the consistence amount of resin per sq area are the primary advantage of pre-pregging. Epoxy resins are also available that can be used specifically tailored for very large applications.
III. Disadvantages of Prepregs
Prepregs typically must be refrigerated until they are used. They are almost always sold only in full rolls. They cost much more than buying epoxy and hand laying the resin. They typically have a short shelf life (6 months is common).
Prepregs should only be used when they are needed. If you can get by without prepregs, typically this is your best option.