 Experimental studies show that applying cashew nut shell liquid, CNSL, on suitably pretreated coir yarns reduces moisture absorption and microbial growth, inhibiting fundal growth on fiber surface by 95%, increasing tensile strength up to 17%, and improving hydrophobicity. The better properties achieved are explained by the selection of coating methodology and interfacial features of the coatings with the coir fiber, indicating potential future application in geotextiles. This article was authored by S. Sumi, N. Unakrishnan, and Lee Matthew.