The Nike(R) Resistance Loop is made of durable material, featuring silicone on the interior to keep the band in place while you challenge your own strength and build muscle. Product Features Durable construction delivers lasting use Silicone on the interior grips surfaces to keep the band in place Knit material feels soft and comfortable Additional Details Recommended sizes by bodyweight: Small: less than 120lbs / 54kg Medium: 125lbs - 170lbs / 57-77kg Large: 175lbs - 205lbs / 79-93kg Materials: 51% rubber/35% acrylic/14% polyester