Wool is well known as the warmest non-petroleum based material, while still allowing breathability, but how do other material types compare?
The following table details performance testing of various knit materials(1). Air Permeability is the rate at which air passes through the material, and Thermal Resistance is the difference by which a material resists heat flow.
| Material | Thickness (mm) | Air Permeability (mm/s) | Thermal Resistance (W/mK) |
| Wool | .837 | 2460 | .027 |
| Acrylic | 1.116 | 1786 | .031 |
| Wool-Acrylic Blend | 1.65 | 1800 | .047 |
| Cotton-Acrylic Blend | .72 | 1653 | .021 |
| Cotton(comb) + Polyester plated | .37 | 296 | .012 |
| Viscose + Lycra plated | .40 | 226 | .015 |
| (Cotton-Bamboo) + Polyester plated | .38 | 293 | .014 |
Technically speaking, a warm-cool feeling that is desired from clothing and blankets, has as much to do with construction type (knit vs. weave) and the relative air permeability of that structure (weave pattern), as it does with the material itself. Because there are so many variations, we've focused on just the material here against a knit base, where all materials had the same loop length and tightness.
Sources
1. http://article.sapub.org/10.5923.j.textile.20170602.02.html