Micro-electro-mechanical systems with fluidic functions rely on micro features typically ranging from 10 to 200 Em in size. To produce these features on polymer substrates with high quality and fidelity, existing techniques typically have long cycle times and are expensive. It has been shown that localized heating with ultrasonic embossing has short cycle times but generates flash. This flash is the result of the displaced material from the feature being generated. The flash is undesirable and must be removed in a post processing step or captured in a special feature designed into the substrate (Flash trap) which limits the design freedom of the sample. This research reviews the elimination of this flash by using micro-cellular foamed polystyrene substrate that self absorb the generated flash. Standard dog bone shaped features were embossed with various parameters and the resulting features characterized by optical and electron beam microscopy. The process studied in detail was ultrasonic embossing and the parameters included: amplitude, engagement force (weld force) and heating time. It was seen that with proper parameters the feature could be fully embossed with no flash. However, because of the availability of materials only a foaming level of 15% was studied which appeared to be slightly too high. This resulted in rough surfaces in the final product.