Elastomeric compositions comprising at least one C4 to C7 monoolefin elastomer, at least one polyalphaolefin, and optionally at least one hydrocarbon polymer additive are disclosed. The PAO comprises oligomers of one or more C2 to C20 alpha-olefins having a kinematic viscosity at 100° C. of 3 to 3000 cSt and a Mw/Mn of less than 4. In one aspect, the elastomeric composition may have improved flex fatigue properties and have a fatigue life of 450,000 Kc or more as measured by ASTM D 412 die C. In another aspect, an elastomeric composition may have improved impermeability and have a permeation coefficient at 40° C. of 160 cc*mm/(m2−day) or less.