Recent Gas Cylinder bottles are now made from STAINLESS STEEL, aluminum, transparent composite materials, instead of the convertional piece of metals.

Don't get it mixed up. Net weight of a Gas Cylinder Bottle is not the same as the "GROSS" weight. The gross weight is what the container weighs when nothing more is to be taken away. While on the other hand, the net weight of gas cylinders is the weight without the material, container it is wrapped in.

Gross weight of a LPG gas cylinder bottle is the total weight, along with the dimensions. A measurement of the height, width, length including the neck ring of the gas bottle. 

To know the gross weight of Gas Cylinder Bottles, just place them on a digital scale. This will give the total weight figure/readings on the dashboard screen. NET weight can't be figure out using the digital scale. However, most gas cylinder manufacturers make it easier by printing the figures on the body of each gas tanks or container. For the 45kg UK propane tanks (Calor Gas), the net weight stamped on body is 47kg. But when placed on the digital scale, it gives 50kg, which is approximately the TARE (gross) weight.