Fast drying merino wool sock with 37.5 technology developed for tropical and warm weather missions. Extra Light cushion underfoot, mesh instep for enhanced breathability, reinforced heel and toe, ankle and arch support. 37.5 active particles supercharge wool's natural abilities by attracting moisture while still in vapor form, before it becomes a sweat droplet. Stay drier longer and increase athletic output. Wool 61% Spandex 6% Nylon 33%