What Makes Soft Yarn?

Soft yarn is a desirable thing in many applications.  Most hand spinners readily acknowledge that less twist in the yarn means softer yarn.  It is absolutely true that low twist yarn will have a softer feel in the skein than the same yarn with more twist.  However, the factor that overwhelmingly trumps any technique used to manipulate fiber softness during spinning is the fiber itself.

A fiber's diameter, with the diameter of individual fibers measured in microns, or thousandths of an inch, is probably the most important predictor of the softness of the yarn made from it.  A thinner "wire" bends more easily than a thick one.  This concept translated to hairs or fibers means that the thin, small diameter hair will yield to the touch more readily and create a less-detectable prickle as skin passes over the fiber end.  Small diameter fiber in a yarn is also more smooth on the surface between fiber ends, enhancing that soft sensation.

A fiber's length, also referred to as its staple length (measured in millimeters), also influences yarn softness.  Longer fiber makes fewer fiber ends to create a prickle in a given length of yarn.

In the real world of natural fibers, a given animal fleece (or batch of vegetable fiber) has fibers of different diameter, all mixed together.  The wool industry depends on testing samples from a given fleece or batch of fiber.  The results are reported on a histogram (for the statisticians in the crowd) which shows for each fiber diameter found in the sample how many fibers had that diameter.  The ideal fleece will have a low average diameter, and most of the fibers will measure within 2 or 3 microns of the average diameter.

The wool industry uses a measurement of the soft-yarn potential of a fiber lot called "comfort factor".  This factor equals the percentage of fibers in a sample that measure under 30 microns.  So fiber with a diameter under 30 microns is soft enough not to create an offensive prickle at the end of the fiber.

Predicting the soft-yarn potential of a given fleece can be greatly enhanced by having a fiber test on it.  Our Cedarbrook fine wool, for example, averages 20 microns, with a comfort factor of over 99%.  This makes for very soft wool.  As the average fiber diameter increases from 20 to 30 micron, the comfort factor naturally drops.  Fiber averaging over 30 micron is not likely to ever make yarn accused of being soft.

If your fiber is under 22 micron average with 98% or better comfort factor, it can probably be spun into yarn that can be worn on the skin.  At higher fiber diameters and lower comfort factors, it is possible to make yarn for acceptably-soft outerwear.  Staple length becomes a stronger factor determining the feel of the yarn at this point.

The bad news is that no fiber measurements can totally predict the characteristics of the yarn that will come from a give batch of fiber.  But for those contemplating what ultimate product to make from a batch of fiber they have no yarn-making experience with, fiber testing is an objective measurement that can help determine the best ultimate use for the fiber and the best yarn to make of it.