The Powder-Snow Reaction is caused by the material PY or PNY, when the standardDistance Parameter is changed to a number less than 0.563. This is because the density of Powder is determined by standardDistance, and Snow seems to provide an attractive force. As the particles get smaller they seem to have less friction, and eventually they start moving on their own.
Snow on it's own is a complex material but combined with Powder, some highly unusual things happen.
AY is a liquid, but PAY is a solid
NY is a solid, but PNY can be a liquidThe material PAY resembles a crystal, almost like ice. It has a repeating structure of particles. The material PNY is a crystal when standardDistance is larger than about 0.55, but turns into plasma below that number. Try it out: fill your screen with PNY, save the file somewhere , open it with a text editor, scroll to the bottom, change standardDistance to 0.5, save, and open it. The PNY will turn into plasma.