Simply remove the sleeve and clean it, using wipes or lukewarm water and regular soap. Ensure the sleeve is completely dry before you put it back on your PENpal. Make sure sleeve is aligned with the buttons and light, so you can see the light fully through the small hole right above the button symbols on the sleeve, and the USB and audio-port through the hole on the side of the sleeve. You may wish to dust the inside lightly with talcum/baby powder to make it easier to put on and remove. Do not use abrasive agents on your sleeve, or put in your dishwasher, as high temperatures or abrasive agents may damage the silicone and make its protective function less effective.