When conditions make communication difficult, Post it® Extreme Notes make leaving notes and reminders easy. Post-it® Extreme Notes are waterproof and strong enough to handle hot and cold environments. They stick indoors and outdoors wherever you need them, making sure what you say stands out and sticks. Made with Dura-Hold? paper and adhesive. These notes stick in hot, cold and wet conditions and stick to rough surfaces such as concrete, raw or painted wood and tile. Not recommended for use on paper or with gel pens.