Because I homeschooled my sons, we have a regular microscope used for high school biology. Like Bellaboo, I was surprised at the mixed results. Most of the mercerized cotton threads (including C&C) were uniform, but one of the very smoothest threads was the polyester serger thread. After all, it's plastic instead of a natural fiber. The fluffiest were the cotton-wrapped polyester. But really, I have used all of them without problem. I sew for hours at a time, so I keep a lint brush next to me and swab out the bobbin casing area every hour or so. Most of the lint comes from the fabric itself, or the batting if I am quilting.