Best material to use to replicate snow???

I am helping a friend of mine build a shelf layout in O-scale. He is including several dioramas along the layout - one of which is going to be a Christmas scene. I’m looking for suggestions as to a best material to use to replicate snow which does not interfere with the operation of locomotives (snow on the tracks, you know!).

Thanks, in advance, for any help!

This is a thread I started some time back that turned out pretty useful. It should answer some questions for you.

http://cs.trains.com/forums/898832/ShowPost.aspx