Low profile external tanks that are form-fitted and sleek. 4 flavours: Fuel, RCS, Battery and Xenon
Specifically designed to fit snuggly around 1Metre tanks/modules in particular, these tanks can increase the endurance capacity of your spacecraft without increasing its girth.
Four versions are currently available: Fuel, RCS and Xenon tanks, as well as the Battery pack
Especially good for final stages and lander modules.
They also work well with the slim decoupler addons, if used during the launching stages.
Maximum of 6x symmetry on 1Metre modules, though 8x works fine on 2+ metre parts
If you want larger versions, simply make a copy, rename to BFT_Form-tank_[TYPE]2 or similar and edit the config file by changing the rescaleFactor to:
rescaleFactor = 2
Then increase the mass and fuel/charge quantities by 8 times. (square-cube law at work