Modified polymer compositions having good flowabilty, impact performance and modulus made from at least one polyolefin (e.g., high density polyethylene or polypropylene) blended with minor amounts of either at least one homogeneous linear ethylene/C.sub.5 -C.sub.20 .alpha.-olefin or at least one substantially linear ethylene/C.sub.3 -C.sub.20 .alpha.-olefin polymer are disclosed. The compositions are suitable for thermoformed or molded thinwall applications such as drinking cups, lids, and food containers where the flow length to wall thickness ratios are greater than about 180:1. A process of making thin wall articles is also disclosed.