It is a non-toxic, water-based acrylic paint designed for use on plastic, metal, and resin miniatures.
Layer paints have a lower pigment density than Citadel Base paints. 
This transparency allows them to be applied in multiple thin layers over darker base coats to build realistic depth, clean gradients, and smooth highlights.
It is widely used as a mid-tone or high-register layer for human skin tones. 
It provides a smooth matte finish and is highly recommended by hobbyists for edge highlighting and layering over a flesh base coat (like Kislev Flesh or Bugman's Glow).