Procion MX Dyes - otherwise known as cold-water, fibre-reactive dyes - are intended for cellulose/plant-based fabrics such as cotton, linen, viscose. Will dye other natural fibres but with varying degrees of colour-depth.
Generally, other dye types (eg Acid Dye) require a heat-source to keep the temperature up as part of the dyeing process, but Procion MX Dyes simply require hot water to start with.
Procion dyes require salt or Urea with washing soda or Soda Ash (depending on which dyeing technique is used) to help the dye to be drawn into the fibre and then fixed there.
Procion Dye is perfect for immersion (bucket) dyeing, tray-dyeing, tie-dye, direct painting techniques, printing (with the thickener, Manutex), batik and shibori.
The Starter Pack contains six mixing colours* - cool and warm versions of red, yellow and blue (as selected by Ruth Issett), 200gms Urea, 6 pipettes, foam brush and easy instructions. (Washing soda or soda ash, salt and Calgon are also required).
* Magenta and Scarlet; Lemon and Golden Yellow; Turquoise and Ultramarine.