Bladders and elastomeric pumps for infusion assemblies are provided. For example, a bladder may comprise a body extending over a length from a first end to an opposing second end； an outer diameter； an inner diameter； and a wall thickness. The wall thickness may gradually transition from a first wall thickness at the first end to a second wall thickness at the second end. In other embodiments, the wall thickness at a midpoint of the length is different than the wall thickness at each of the first end and the second end. An elastomeric pump may comprise an inflatable elastomeric bladder and a mandrel. The bladder includes a body extending over a bladder length from a first bladder end to an opposing second bladder end and a wall thickness, which is different at a midpoint of the bladder length than at each of the first and second bladder ends.
