Valves and methods for manufacturing the valves are disclosed. The valves are formed from a plurality of flexible polymer layers. A radio frequency bonding process, or the like, is utilized to form welds between the various layers. In general, a sub-assembly is formed that includes a valve layer bonded to a substrate layer. The sub-assembly is bonded to a second element such that a channel is formed between the valve layer and the second element. The channel includes an inlet, an outlet, and a pair of weld beads located in the inlet that place the inlet in an open configuration.