Rubber sole - COMFORTABLE, FOR-EVERYTHING SHOE - Whether youre out on a run, trying out a new trail, hitting the gym, or toeing a slackline, youll love the Prios combination of freedom and protection - XERO DROP SOLE FOR PERFECT POSTURE - The Xero Drop sole offers a non-elevated heel and is low-to-the-ground - this allows proper posture, balance, and agility for all-round performance - ULTRA-THIN BAREFOOT DESIGN - Wear with or without socks. The optional 2mm insole lets you have more or less of a barefoot feel depending on your mood - VEGAN FRIENDLY - Xero Shoes believes in promoting healthy and sustainable lifestyles which is why the Prio is made with zero animal products - GET THE RIGHT FIT with FREE Domestic Exchanges - This shoe runs 'true to size."