Glass containers have been replaced to a greater extent with plastic containers as they are lightweight and stable against breakage. Nowadays, glass is used only for those products that are not compatible with plastic. Plastics are polymers that can be shaped when softened and then hardened to produce the desired shape and structure. Flexible containers fabricated from modified polyethylenes, polycarbonates, polypropylenes, polyesters, polyolefins, teflon and polyvinyl chlorides are used in parenterals.