SES primarily produces non-woven membranes from sub-micron diameter fibers using an EHD phenomenon of jet instability, often referred to as "whipping" . After an applied voltage generates surface charges that overcome the drop surface tension, a jet (i.e., a fluid column) is ejected that is initially straight. As the surface charges on the jet surface increase in density along its length towards the collector , they further stretch and spiral the jet to form small diameter fibers. SES membranes are non-woven as jet whipping makes it difficult to place fibers in a specific location.