US Patent 7314661 Synthetic closures having improved physical properties

The synthetic closures disclosed herein are made from novel compositions that comprise a thermoplastic elastomer, polypropylene, a foaming agent, and a plurality of gas-encapsulating thermoplastic microspheres. Without necessarily prescribing to any scientific theory, it is believed that the gas-encapsulating thermoplastic microspheres in combination with the other ingredients provide a feed material especially useful for manufacturing synthetic closures having an appropriate combination of physical properties like, for example, density, oxygen permeability, hardness, extraction or removal force, compression percent recovery (over selected periods of time), and compression force (to compress closure to a smaller diameter).