Wet vs. Dry Carbon Fiber

Wet carbon fibre means carbon fibre has been impregnated in epoxy by hand, and ususally cured in an oven, or even at room temperature, and the terminology of “wet” carbon fibre is beceause in the process of manufacturing the part, you actually have to manually “wet” the carbon fibre cloth with epoxy. Infusion is a wet carbon fibre technique wich consist of infusing the carbon fibre with epoxy resin by “soaking” epoxy into it while the part is under vaccum pressure, wich often produces better results when mastered than just applying resin directly onto the cloth while laying it up into the mold.

Dry carbon fibre is a completely different process, wich consist of having “pre-impregnated” (also reffered as prepreg) fibres. This means the carbon fibre cloth is already impregnated by resin by manufacturer. Prepreg carbon fibres usually need to be stored at -20°C to not cure by themselves at room temperature. Then, in most cases, the prepreg part is cured in an Autoclave. This results in better quality parts for various reasons, mostly beceause more pressure applied on the part during vaccum, and thus reducing the resin/fibre ratio needed in the part. This is reffered as “Dry” carbon fibre beceause you do not actually need to manually “wet” the carbon fibre witih epoxy since they are already pre-impregnated.

Dry carbon fibre is a very costly process, beceause first, you need an autoclave, prepreg carbon fibre is way more expensive than just buying carbon fibre cloth and epoxy, and then, the molds and vaccum tooling need to be of higher quality and high temperature resistant since prepreg usually need to cure at higher temperature than usual lamination epoxies. For example, you can realise a mold for a “wet-layup” process with just a gelcoat and some polyesther, while you’d use an aluminum machined mold for high temperature autoclave applications.

Mostly, the strenght of carbon fibre depends of the density of the part, wich is greater in dry carbon fibre parts beceause of the autoclave curing process, is highly dependent of curing temperatures and propreties of the epoxy used itself. Strenght comes from the carbon fibre itself, so, more fibre – less resin is a must, but not too low to avoid “air voids” into the part wich would cause structural issues. Autoclave allows for a lower resin/fibre ratio without having structural problems beceause the higher pressure in the autoclave vaccum increases the “compactation” of the part.

As for surface, you can apply a glossy layer of gelcoat to a dry carbon fibre part, and you can have a matte finish in a wet-layup process. Mostly, the glossy/matte finish is depending if your mold has a matte or glossy finish, or you can just simply grit with soft sandpaper a glossy part to get a matte finish.

For maintenance, it actually depends more if the part has a gelcoat or a varnish applied to it or not. If not, the fibres are closer to the surface, and you’d risk to damage it by using inappropriate products. Gelcoat-Varnish parts are actually better protected.