We don’t use any toxic sealants for our Silipint cups so sometimes (though rarely) the silicone can stain with certain acidic drinks, such as coffee. The best way to avoid this is to choose a cup color that won't stain with your drink. You can also reduce staining by immediately cleaning you cup after use.  If you have a stain that seems to have set in we recommend soaking your cup in 3% Hydrogen Peroxide for 24 hours.  If these tricks don’t work and you're unhappy with a staining situation, we will replace your product, minus shipping charges. Email us at support@Silipint.com.