Sustainable technical textiles made from coir natural fibers are considered an alternative material to synthetic fiber-based textiles. Coir fibers are environmentally friendly and have better durability compared to other natural fibers. The fibers interact with other materials and/or fibers themselves during the manufacturing process and/or in service. Understanding the friction characteristics will help in the design process and improve the life of textiles made, and the current work is focused on this. Friction testing of natural fibers is challenging due to their size and fragility. A novel in-house tribometer based on the capstan method, where individual coir fibers were slid against a polyamide cylinder, was utilized in the current work. The friction behaviour of untreated oven-dried and alkali-treated single coir fibers was investigated under sliding conditions. Alkali treatment was used to improve the mechanical properties of coir fibers and modify the surface of the fibers. Although alkali treatment increased the surface roughness of coir fibers, there is only a marginal increase in the friction coefficient. An inverse relationship between applied load and friction coefficient for coir fibers, where the friction coefficient decreased with increasing load, was observed. This study contributes to the understanding of natural fiber friction and provides insight to use in sustainable technical textile applications.