I've always used woven carbon fabric, but I keep seeing unidirectional mentioned for structural parts. When is it actually worth switching to unidirectional, and what do I gain by doing it?
The choice comes down to how the loads run through the part. Unidirectional carbon puts every fibre in one direction, so it gives you the most stiffness and strength along that axis for the least weight, and you build a laminate by orienting each ply to match the load, for example 0, plus or minus 45 and 90 degrees. Woven fabric carries fibre in two directions at once, drapes more easily over shapes and is quicker to handle, but the crimp where the tows cross costs a little stiffness. For a weight-critical or heavily loaded part where you know the load paths, unidirectional is usually worth it. For complex shapes, multi-directional loads or cosmetic work, woven is often the better all-rounder. If you tell us about the part and how it is loaded, we can suggest a sensible layup.
Ask the Allbase team and we'll add the answer here for everyone.