Fiber Testing

1. The Count System is based on the number of hanks of yarn (560 yds each) spun from one pound of wool. Values are from 36's - 90's with the numbers corresponding to the number of hanks per pound. Lincoln & Cotswold sheep (coarser wool) are in the 36's and Merino sheep (finer wool) are in the 90's.

2. The Blood System is the oldest measuring system and it is based on the percent of Merino or Ramboullet blood present in a particular fleece or sheep.

3. The Micron System was developed by USDA's Denver Wool Laboratory. It uses 16 grades ranked according to fiber diameter in microns. This system is used for llamas & alpacas.

Yocom-McColl Testing Laboratories, Inc. used the micron system to evaluate fiber diameters of core samples, top samples and individual animal samples using LaserScan analysis. Samples are cut into 2mm snippets and placed in a solution of isopropyl alcohol and 8% water. Fibers are pumped through a laser cell that measures the fibers and analyzes the diameter. Two thousand fibers are measured in about one minute.

The results of a laser scan analysis are reported in a histogram along with numerical values using I.W.T.O. (International Wool Testing Organization) Method 12 or 24. The numerical values reported are the micron count or mean fiber diameter, the standard deviation (SD), the coefficient of variation (CV), and the prickle factor. Ideally, the histogram should be very tall and narrow rather than short and wide. The micron count reported is the average diameter of all the fibers in the sample which measures the central tendency of the fiber. The standard deviation (SD) indicates how the fiber diameters vary around the mean. The smaller the standard deviation the less variation among the diameters of the fiber. The ideal standard deviation will vary with the average fiber diameter. For example, the ideal SD for 17 microns and 25 microns is 4.25 microns and 6.25 microns respectively. The coefficient of variation (CV) is the percentage of variation in the measurements of average fiber diameter or micron count and SD. Coefficient of variation is calculated by dividing SD by micron count and then multiplying by 100. Twenty-five percent or less is desirable. This value is a unitless number which enables various populations to be compared to each other. The prickle factor is the % of fibers in the sample that are over 30 microns. Testing has indicated that fibers 21 microns or less tend not to prickle when worn next to the skin, and that fibers over 30 microns always tend to prickle.

Last updated on February 8, 1997