Clear Ultra Non-Latex Orthodontic Elastics are made from a medical grade resin.  Our Non-Latex Elastics out-perform all other all other elastics and are crystal clear appearance. Every package is checked to ssure all cuts are consistent and that the forces are correct.  Will not absorb water. The different weights are in reference to the "weight pull" on the elastics.  Other popular uses include: dog grooming elastics, doll hair elastics, cornrow elastics, small rubber bands for crafts, hair elastics.