A flat bag has no capacity. Capacity is a three dimensional concept and so the bag must have a length, width and height. Also, to calculate its capacity, it is necessary to know the shape of the bag.
A 12-sided flat-shaped fragment is a dodecagon.
So it doesn't roll off when you place it on a flat surface.
Dodecagon
A decagon.
An icosagon
DUNE
A flat three sided figure is a triangle.
A 6 sided hexagon perhaps
= Septagon = A 7-sided polygon (a flat shape with straight sides). (Also called Heptagon)
a triple heptagon.
DUNE
they changed it because they were to lazy to walk up steps so they changed it to flat sided because they wanted to get their motorized wheel chairs up the side