What Lab-Testing Our Wool Actually Means
Every lot of wool roving sold by The Beartooth Homestead in Billings, Montana is tested at the Montana Wool Lab at Montana State University. When I say that, I'm describing something specific: a standardized procedure that produces a set of numbers telling you exactly what the fiber is before you commit to a project.
Here's what those numbers mean.
The Procedure: ASTM D6500 Using OFDA 2000
ASTM D6500 is a standard test method for measuring fiber diameter using the Optical Fibre Diameter Analyser (OFDA). The OFDA 2000 is the instrument used at the Montana Wool Lab. It works by measuring thousands of individual fiber snippets from a sample and producing a statistical profile of the fiber population in that fleece.
The test is objective. It doesn't depend on who's running it. The same fleece sent to two labs using the same method should produce the same numbers. That's the point of a standardized procedure.
Micron Average: What "Fine" Actually Means
Micron average is the most cited fiber number because it has the most direct effect on how the finished yarn or fabric feels against skin. One micron is one millionth of a meter. Human hair typically runs 60 to 80 microns. Fine wool runs well below that.
The fleeces in our flock range from 20.8 microns (Dahlia) to 25.2 microns (Sally). To put that in context: merino wool, the standard reference for "soft wool," usually runs between 17 and 22 microns. The finer Targhee and Rambouillet crosses in our flock land in similar range.
Below roughly 25 microns, most people can wear wool directly against skin without irritation. Above that threshold, more fibers begin to prickle. That doesn't mean the wool is lower quality, it means it's better suited for certain applications. Sally's fleece at 25.2 microns is excellent for outerwear, rugs, and felting projects, where durability and structure matter more than next-to-skin softness.
Comfort Factor: A More Useful Number
Comfort factor is the percentage of fibers in the sample measuring below 30 microns. Fibers above 30 microns are the ones that cause prickle sensation on skin. A comfort factor of 96% means 96% of the fibers in that fleece are below the prickle threshold.
This number is often more useful than the average because it tells you about the distribution, not just the center. A fleece with a 22-micron average and a high standard deviation might have enough coarse fibers to prickle even though the average sounds fine. Comfort factor captures that risk directly.
In our flock, Daffodil runs 96.1%, Mabel runs 95.9%, and Dahlia at 20.8 microns runs 95.5%. Sally's comfort factor of 84.5% is lower, consistent with her slightly coarser average, which is why we recommend her fleece for non-next-to-skin projects.
Staple Length: Matching Fleece to Technique
Staple length is the average length of an unextended fiber lock, measured in millimeters. It matters primarily for spinning technique. Longer staples suit worsted-style spinning, where fibers are combed parallel and then drawn out. Shorter staples suit woolen-style spinning, where fibers are carded and left more random.
Daffodil's staple of 120mm is the longest in the flock and makes her fleece well-suited for worsted preparation and weaving. Mabel and Dahlia both run around 75mm. Sally at 60mm is on the shorter end for a Targhee cross, which contributes to her suitability for felting and dense structural work.
What This Means for Ordering
When you order roving from The Beartooth Homestead, you're ordering by individual animal. Each listing names the sheep, the breed, the price per pound, and the test numbers. Availability is limited to 2 lbs per sheep per season, and not every animal's fleece is available every year depending on condition and timing.
If you're not sure which fleece is right for your project, reach out through our contact page and describe what you're making. That's usually the fastest way to get to the right answer.