42% Cotton, 39% Superwash Merino Wool, 13% Polyamide nylon, 6% Elite Elastic

From KnitPicks.com:

Risata means “laughter” in Italian because this yarn will delight you to giggles while you knit with it. Animal fibers and plant fibers require different dye types, so this yarn has been through the dyeing process twice - once for the wool and again for the cotton. The result is a visually textured tonal twist that gives the solid color a lot of character. There are two miniscule strands of elastic in the center, around which the cotton and wool plies are wrapped. The cotton contributes coolness, making Risata ideal for summer and warm climate wear. The elastic allows stretch, compensating for the lack of stretch in the cotton, and the nylon adds strength. You’ll love the spongy soft feel as socks in Risata cushion your feet. A long-wearing, machine washable sock yarn perfect for kids and grown-ups.