Moisture is the enemy of any delicate optic, and with the Farpoint Astro Desiccant Cap you can protect your telescope from moisture getting into and collecting inside your closed optical tube assembly (OTA), such as refractor and catadioptric designs that tend to trap moisture. This cap replaces the simple standard dust cap that you usually use at the end of your 2" focuser drawtube or visual back with the added benefit of disposable moisture-absorbing silica gel desiccant that prevents the ingress of moisture. The cap is made of lightweight and durable anodized aluminum and comes with five gel pouches that indicate when they need to be changed, plus a cap for the end to prevent the silica from absorbing ambient air moisture when you're using your telescope. When you run through the five that come with the cap, you can get 20-pack refills separately.