Roof Protectors / Skyliners
Tent Roof protectors have a number of different purposes but mainly to extend the life of your tent as well as improve it.
Ultroviolet rays are one of the biggest killers of tents and which can degrade your tent over its life, this is certainly more prominent when camping in warmer climates such as in southern parts of Europe. Roof protectors aid this by protecting this area from UV rays.
They also very good to use if you have pitch under a tree where tree sap or bird feces may land on your tent, so makes it easier to clean as well.
Most roof protectors are designed for specific tents so make sure you choose the correct one for yours.