Water is pumped to the filter and then to the solar collector, where it heats up before returning to the pool. The collector(s) may also be used in hot climates to cool the pool during peak summer months by nightly circulating the water through the collector. Some solar heating systems include sensors and an automatic valve that diverts water through the collector(s) when the temperature of the collector is sufficiently higher than that of the pool. When the temperature of the collector is close to that of the tank, filtered water bypasses the collector and is returned to the water. Solar panel collectors are made of various materials. The type you will need depends on your climate and how you will be using the collector. If you only use your pool when temperatures are above zero so you will need only an unglazed collection device. Unglazed collections do not include a glass (glazing) mask. These are generally made from heavy-duty rubber or plastic treated with a light ultraviolet (UV) inhibitor to prolong the panel life. Unglazed collectors are typically less costly than glazed collectors, because of their cheap parts and simple design. Even in cold climates, such unglazed solutions can work for indoor pools if the system is designed to drain back when not in use. Even if the system needs to be shut down during cold weather, unglazed collectors may be more cost-effective than implementing a more costly collector glazed system.