Lyra is referring to dust explosions. This is a hazard in coal mines, where coal dust explosions are common. But any powdered combustible material in an enclosed atmosphere can result in an explosion. This includes materials commonly known to oxidize, including mundane items like sugar, powdered milk and flour.
As seen in the video, flour will even explode if it's thrown with some force into an ordinary campfire.
Coal-silk seems to be the name given in Lyra's world to nylon or other manmade fibres. Lyra also mentions that the bag she recieved from Mrs Coulter when living with her in London was made from coal-silk.
It is one of the subtle differences between Lyra's world and our own. Nylon only became commonly used in our world from World War 2 onwards; like knowledge of particle physics, it is one of the things doesn't seem to fit with the Victorian-style world that Lyra lives in, dependant as it is on steam power.
Snow is a great insulator, and the children's chances of surviving the night by doing this would be fairly good. There's an interesting article here about surviving the extreme cold which mentions building snow shelters.