What are optimal fabrics for cycling clothing?
Wool, particularly Merino wool, is tough to beat. It's partially hydrophilic, cooling you by wicking sweat away from the skin while also retaining warmth when wet. It's lightweight, soft, and has natural mild antibacterial and antifungal properties that reduce the amount of funky odors.

The main downside compared to synthetic fabrics is probably cost, especially for cycling-specific apparel.