Sandbags are a miniature wargaming terrain essential. Michael Blair has this advice on making them.

Sandbags

This works for 25mm scale and maybe 20mm but would not work for 6mm unless you leave out the bandage. This is not my method, it came from the net or the list but it works well and is the one I use. Beans of chewing gun just does not look right to me, so I have to do it the hard way.
Material Components
Das air drying clay or equivalent
Crepe bandage, width approximately 1″
PVA glue, more or less diluted.

Tools
Flat surface (glass is ideal)
Scissors
Polytheme sheet (optional)
Cling film (possibly)
old paint brush

1. Roll out the Das into a sausage maybe half the diameter of a finger and then roll it onto the
stretched out bandage. You may need to add a little of the diluted PVA to make it stick.

2. Cut the bandage wrapped sausage into sandbag sized lengths. While still wet place them into position,
moulding them over each other and piching the ends closed as best you can. Brush the dilute PVA over
them. You might want to set them on a sheet of plastic to make them easier to lft once they have set. For a
vehicle putting a piece of cling film below them should allow them to set in place and be a good fit
but be removable for painting and so on.

They will take some time to dry but they look wonderful and could be used as masters for making
moulds.