Difference between carded and combed yarn process?

If the yarn is spun in the direction of the fibers a smoother yarn is produced than if the yarn is spun perpendicular to the fibers.

Carding removes tangles in wool fibers but does not fully align the fibers so they are all going in exactly the same direction. Most may be going in one direction but there will always be some going off in their own direction. If the carded fiber is spun with most of the fibers going in the direction of spinning (ie toward the spinning wheel), it will produce a more compact, smoother yarn. If it is spun with most of the fibers perpendicular to the direction of spin, it will produce a fluffier, airier yarn. However, because there is always some haphazard arrangement of fibers that have been carded, carded wool will always produce fluffier yarn than combed wool. Fluffy or airy yarn is generally best suited for knitting.

Combing is much more labor intensive. Fine toothed combs are used to straighten and align each individual fiber parallel to the direction of spinning AS the fiber is being spun. Unlike carding, combing cannot be done ahead of time. This produces a very smooth, very compactly spun yarn which is best suited for weaving.

When cotton or another fabric is "combed," the shortest, additional fibers of a batch are removed. The result produces high-quality, extra soft yarns with Excellent strength and softness. Combed cotton uses finer fiber than carded yarns and is more regular and expensive than carded yarn.