Interfacing is meant to add some stiffness to the fabric, so it's good for making shirt collar hold it's shape, or shoring up the edges of a tank-shaped top to keep the neck & armholes from gaping open, or keeping a waistband from rolling.

A lining fabric is probably a better choice for simply adding some weight without stiffening up the fabric. Just make sure that the clean requirements of the lining are compatible with those of the fabric you wish to use for the flashes. Lining fabric is typically made from polyester, cotton, poly/cotton, or silk, but you can use whatever works in your situation.