Traditional solvent based or PU based inks are not reliable for printing on the silicone surface. The surface energy of silicone is very low which the reason why the inks can not adhere to the silicone surface which makes the intermolecular forces very low. The intermolecular forces that contract the surface are termed surface tension. Surface tension, a measurement of surface energy, is expressed in dynes/cm. http://www.xysiliconeink.com/s....ilicone-ink/hd-silic