The DrawnBy: markers are oil-based and have a shelf life of 18 months if unopened. Please do make your best effort to cap the markers properly as they dry out very quickly in Singapore's humid weather.If you find that the markers are starting to dry out, you may try dipping the nibs in rubbing alcohol to try and reconstitute them. The coloured portion of the markers can be separated from the plastic body for you to drip a couple of drops of rubbing alcohol inside the barrel as well. Do avoid putting too much as the rubbing alcohol thins the ink and will affect the colour quality.If this doesn't work, fret not! DrawnBy: markers are available as a stand-alone purchase from our DrawnBy: Washable Silicone Drawing and Colouring Mats :)Care FAQ