The difference between the Silicone and Surgical steel, other than the material, is that the Silicone is smaller and square in diameter, whereas the Surgical Steel is larger and circular in diameter. We typically recommend these cartridges for those who are unsure of Micro-Needling or for those who may have contraindications to Micro-needling. The Silicone cartridge is great to use as an add-on for eye treatments, as is it is safe to use all the way down to the lash line on the lower and upper lid to help stimulate lash growth. For a full-face Nano treatment the Surgical Steel is recommended.