 To improve the adhesive and hygroscopic qualities of the paint, as well as the flexibility of the rather brittle paint layer after drying, propylene glycol is often added.Gouache differs from watercolor in that the particles are typically larger, the ratio of pigment to binder is much higher, and an additional white filler such as chalk, a "body", may be part of the paint.This makes gouache heavier and more opaque, with greater reflective qualities.