From the outset, Castelli Nanoflex Knee Warmers look and seem like most medium weight knee warmers. However upon close inspection and initial use, the Nanoflex fabric and construction details take them to the next level. The Nanoflex Knee Warmers are designed to be used in slightly colder temps and for inclement weather. Perfect for days when you want protection but tights are a bit much. To understand how well these work in the right conditions, you need have an understanding of the Nanoflex textile.
Nanoflex starts out as the Castelli Thermoflex fabric. This fabric is then treated with a 5 layer microfilament coating that provides a weather barrier. Thermoflex + proprietary microfilament coating treatment = Nanoflex.
This Nanoflex treatment consist of a coating that is constructed from millions of microscopic filaments. The grouping of these filaments provide protection from wind and water, but are just porous enough to release moisture and perspiration from within. Nanoflex is soft and elastic which leaves the garment feeling comfortable yet supportive. Etymology of Nanoflex comes from combining the metric prefix nano with the word flex. In this case Nano means many and flex refers to a soft flexible fabric. Now combine nano with flex and you get Nanoflex, the magical material that provides millions of microfilaments that coat the thermal based fabric Thermoflex. This Nanoflex/Thermoflex combo provides ample protection from the elements in a flexible and comfortable garment. The amount of breathability vs wind and weather protection is unrivaled.
These Nanoflex Knee Warmers were designed to work in the wide 45-65ºF temperature range, so you should get plenty of use out of them. Note the silicone grippers detail on the top of the warmer. Castelli was clever to place the gripper on the inside and outside, so the warmer holds the warmer from sliding down your leg and the short leg from slouching simultaneously. Nanoflex works best when it is a snug fit, so do not expect these to feel loose with bunching and a gathering of material. They are designed to fit tightly.