This is a glass tube, which is specifically designed to be used with the Aspire Atlantis Tank Kit with the Sub Ohm Coil. It is made of pyrex and can be used with many different types of e-liquids as long as it is used in the specified tank. This means that you can choose exactly the strength, the flavor and the type you want without worries that it may not be compatible with your glass tube. It can be used to replace a broken glass and so it is useful to have some of these spare just in case you do, particularly if you are accident prone or have already managed to break one. They are strong, but as they are made of pyrex, they will break if they are dropped from a height, thrown or stepped on, so you will need to be careful with them and look after them.