Polyolefins are polymers composed of simple alkenes, with the most notable being ethylene and propylene. With both polyethylene and polypropylene different grades are available. Polyethylene has varying densities whereas polypropylene has varying locations of the methyl group. Polyethylene is used in applications such as packaging, filters, underpads for hospital beds, and heart valves. Polypropylene is used in applications such as syringes, drapes and gowns, packaging, and sutures.