What is the best materials to make snow on minatures?
Like many things to do with miniatures, there are things you can buy and things you can make.

Buy

You can buy what's known as modelling snow from most manufacturers of scenic products. This is likely to contain crushed glass, but does save you from crushing it yourself.

Make

The other well known material for making snow is Bicarbonate of Soda (AKA Baking Soda) - available at virtually every food shop or supermarket. This looks great at first, but over a period of a few years becomes increasingly yellow. 

I've also heard of people using flour...don't do this. It's too coarse, and has a tendency to rot if you're not careful.


      Image from a basing tutorial I wrote a few years ago showing snow made with bicarbonate of soda.

I also recommend that you use water effects (clear resin) to stick the snow down instead of PVA, it looks better.