Our mil-spec sport sock is the same sock knit for the US military, including the use of anti-microbial silver filament yarn knit into the heel, toe, and sole. Silver is proven to kill bacteria and promote moisture migration and is a game-changing technical addition to this super hard wearing cotton sock. For added performance and comfort, we went beyond military spec and added a compression band on the foot and additional arch support. You can hike for days in this sock and your feet will be well supported and the silver will fight off the stink. The "original" 4 pack includes one of each original color - safety orange, navy, coyote and black - while the "new" 4 pack includes one of each new color - olive, grey, denim and oxblood. You can also now select an "all black" or "all navy" 4 pack at checkout. Or, crush a 10 pack, which includes one of each color we make - white, yellow, grey, olive, coyote, oxblood, orange, denim, navy and black. To customize your pack just leave a note at checkout or drop us a line at firstname.lastname@example.org.