You'll want to wash your flask before its first use. Use a warm soapy water and a soft towel. Stay away from using a papertowel, a microfiber towel may be preferred. You can draw a little bath of soapy suds and wipe it about. We use microfiber towels, and a dish soap. The soap helps soften the wash so that your towel slides against the exterior of the flask instead of rubbing and grinding against it. Little particles unseen by the naked eye, hiding in the towel or the flask can work together to work as sandpaper. 

Once done, use a dry towel to wipe off excess water.  Let air dry till remaining water evaporates. Once complete, you be left with a nice clean flask. You can do this with our stainless steel flasks as well as those wrapped with vinyl.