Microfluidic hydrodynamic focusing of an alcohol/lipid mixture into a narrow fluid stream by two oblique buffer streams provides a controlled and reproducible method of forming phospholipid bilayer vesicles (i.e., liposomes) with relatively monodisperse and specific size ranges. Previous work has established that liposome size can be controlled by changing the relative and absolute flow rates of the fluids. A kinetic (non-equilibrium) theoretical description of the detergent dilution liposome formation method was developed previously, in which planar bilayer discs aggregate until they become sufficiently large to close into spherical liposomes. In this work, we use the kinetic theory to predict that the temperature should change the liposome size primarily as a result of its effect on the membrane bending elasticity modulus. In agreement with theory, our experiments show larger liposomes forming at or below the transition temperature, and a much smaller dependence of size on temperature well above the transition temperature, where the elasticity modulus is relatively constant.