Cost-effective fabrication of microfluidic networks require that all components have to be manufactured with up-scalable processes such as reel-to-reel fabrication of foil-based devices. A microvalve design must take into account functional requirements together with manufacturing feasibilities. Here we present the development of a modular polymeric laser structured microvalve. The complete valve structure is designed to be used in a bendable lab-in-foil system. The modular microvalve design consists of three layers: an actuator layer, an interfacing membrane, and a passive microchannel layer to be separately fabricated and then stacked. Different actuator layer concepts are compared out of which a thermal actuation scheme generating sufficient stroke using phase changing paraffin is chosen. The passive layer is designed with a shallow and sufficiently smooth spherical cavity that acts as the valve seat from which paraffin material can reliably retract during solidification. The shape and dimensions of the shallow cavity are derived from the natural membrane deflection and from the channel cross section. It is not essential that all the paraffin within the actuator cavity to be molten for valve closure allowing a high degree of assembly tolerance and inherent sealing of actuator cavity. All the module layers in the current prototype are structured using 3D laser fabrication processes but mass-fabrication methods like reel-to-reel hot-embossing are foreseen as well. A prototype microvalve stack was assembled with a thickness of 1.1 mm which could be further reduced to meet the requirements of extremely flexible lab-on-foil systems. The closed valve is tested up to a pressure of 3 kPa without any measurable leakage. The dynamics of valve closure is evaluated by a new optical characterization method based on image processing of color micrograph sequences taken from the transparent valve.