Medium Weight Medical-grade synthetic polyisoprene. Consistent force up to 500% elongation. They are manufactured here in the United States. Features & details High-quality Latex-free grooming elastics - approx. 100 count - sold by weight not counted manually so number of pcs is approximate. Space age material outperforms Latex and rubber. Will not become sticky like rubber or absorb water like Latex. Will not cause allergic reactions. Other uses: dog bows, doll hair, corn row bands, horse manes, craft use. The sizes normally used for tying dog hair daily is 5/16 / 3/8 and 1/4 the smaller sizes are usually used on show days and on bows.