Advice on heat shields

Had a bit of excitement this week, heat shield caught fire.

http://www.landyzone.co.uk/lz/f10/fire-hazard-124114.html

I'm thinking of making my own now rather than getting a standard set. I've got some silicon rubber tiles at work which are used for heat protection and I was wondering if anyone knows if they can take the temp from cats which (as I've just learned) can get hot enough to glow? My idea is to use the silicon on the car's underbody, then a layer of glass wool, then some thin sheet steel facing the cat to reflect part of the heat back down.

Would appreciate if someone could tell me actually how hot the cats can get and at what temp silicon fails. Or if you've any better advice on how to make the shields or if you know where I can buy uprated shields from the genuine ones?

Cheers!

dont use standard glass wool it will burn what you need is something called rockwool as its made from some kinda volcanic rock and is used to gain a 3 hour fire barrier in the floors for loft conversions but before you use the stuff for a heatsheild burn it with a blowlamp to get the smell out of it otherwise itll stink the cab out for weeks

Handy tip, cheers! I'll let everybody know how I get along.