The coolest and most breathable fabrics for sleepwear are natural organic fibers and advanced botanical textiles that offer exceptional moisture-wicking properties and thermal regulation. Linen, 100% lightweight cotton, bamboo viscose, and modal (or Tencel lyocell) are universally recognized as the best cooling options. These materials allow air to circulate freely against the skin, absorb perspiration rapidly, and evaporate moisture quickly, preventing night sweats and maintaining a comfortable body temperature throughout warm nights.