Thermochromic Banger

A Thermochromic Banger is a thermal styled bangers which contains a colored sand in between the two walls. The colored sand (typically yellow)  changes color as the temperature changes. The slight change in color of the sand within the Thermochromic banger, is used as a temperature gauge, so once you understand the shade of color you prefer (the temp you like) it's easy to see once the banger has reached this temp.

There are more accurate modern methods for banger temperature reading, such as the Terp Timer and the Terpometer, amongst others which can be seen by clicking Banger Temperature Reader.