The carbon fibres[CF] are what gives the CF parts their strength, the resin just holds the fibres to the moulded form. The CF can come from several sources. I gather the CF that I use, comes from carbonising a Polyacrylonitrile[PAN] precursor. There also seems to be CF made from a pitch precursor, the properties of these are poor compared to the stuff made from PAN. I was told a lot of the cheap imported stuff is made from pitch and stories of Russian CF that was burn't cloth! how true that is I don't know.

CF is available with different properties, such as strength and modulus. I have always bought HT [High Tensile] as far as I know.

The individual fibres are very fine, a lot finer than a hair. Each fibre in the weave is made up of a lot of individual fibres. I tend to use 200 gm metre sq 3K[?] twill, I am not sure what the 3k refers to, 3 thousand fibres per bundle?

The fabric comes in lots of styles, basically you find three: plain weave, twill weave and unidirectional, there are many more but these 3 are the ones you are most likely to come across. If you look at some exhaust cans satin weave has been used, you can see a large diamond pattern.

1. Plain weave is very stable, you can cut a shape out and it doesn't fall apart, there is quite a bit of crimp to the fibres and isn't as easy to drape around compound curves as the other styles, however the weave holds its shape excellently.
2. Twill this is where a fibre goes under 2 fibres and over 2 and so on, that is 2x2 twill. Twill drapes around curves better than plain weave, it also seems to wet out better than plain weave, there is less crimp than plain weave so it should be stronger but the fabric falls apart very easily and it is quite hard to keep the weave straight. Generally I prefer twill because its easier to wet out and drape and I just accept the fraying.
3. Unidirectional I used this once or twice, so my experience is limited. All the fibres point in the same direction hence 'UD'. The stuff I had, had a yellow fibre stitched across it every 6" to hold it together. I used this fabric where the part had all the force in one direction, UD puts all the fibres in the direction I wanted. It was terrible stuff to use, I wasted twice[easily] as much as I used and it ended up quite messy. However for some things I can see there is not really any other choice.

I have an SPS reinforcement guide it outlines all the styles and materials that are available and explains some of the characteristics. I buy glassfibre and Kevlar twill, I assume any type of fabric can be bought in any style. There are also hybrid fabrics glass/carbon and carbon/Kevlar.

The drapeability will be very important if you use a lot of compound curves. I have tried reducing the curves in mudguards but it can still be quite a job trying to get a plain weave fabric into the mould, especialy if your trying to get it done fairly quickly. Twill is much easier to use and faster to get in the mould, unless the mould is very simple. Twill also wets out easier and you get less pinholes, pinholes occur at the intersection of warp and weft, as there are less intersections there will be less pinholes.

For polyester/glass moulds I use chopped strand[CS], this is random chopped lengths of fibreglass bonded together in to a mat, CS builds thickness quickly that is about all I can say about that.

Weight. Fabric thickness is in gm per square metre, I use 200 most of the time this is about .25 mm thick. I have had 360 gm it was difficult to use. and I have had 60 gm Kevlar, this is very thin.