A method for forming a fiber, the method comprising charging to a reactive extruder a first polymer and a second polymer to form an initial blend, where the first polymer is a propylene-based elastomer including up to 35% by weight ethylene-derived units and a heat of fusion, as determined according to DSC procedures according to ASTM E-793, of less than 80 J/g and a melt temperature of less than 110° C., where the second polymer is a propylene-based polymer having a melt temperature in excess of 110° C. and a heat of fusion in excess of 80 J/g, and introducing the reactive blend to a spinneret to form a fiber or extruding the reacted blend through a plurality of die capillaries to form molten threads or filaments which are attenuated in a gas stream to form meltblown fibers.