A method and an apparatus for forming a plurality of polymer layers via a plurality of slots (60), wherein the plurality of layers are combined to generate a multilayer polymer flow stream; and controlling heat flow to the plurality of slots in conjunction with the formation of the plurality of polymer layers. The multilayer polymer flow stream may be used to generate a multilayer film. In some embodiments, the cross-web layer thickness profile may be controlled by controlling heat flow from heaters (54a, 54b) to the plurality of slots that form the plurality of polymer layers.