The main areas one would use foil faced glass wool products would be for heating pipes in commercial buildings, boiler rooms and steam pipes.
The glass wool itself can cope with temperatures up to around 300ºC, although the binder will begin to dissolve around 225ºC + - this will not stop the product actually working, but it will become softer and lose much of its mechanical strength. It is suitable for many indoor applications, excepting those where dust and fibres are unacceptable, but like any other mineral fibre it should not be used externally. Mineral wool has an open cell structure, and as such will absorb moisture. Any insulation works on the principal of trapping air, as still air is a very good insulator, but if you replace that air with water, with is a very poor insulator, then it ceases to function. In the case of frost protection applications, a wet insulation is often worse than no insulation at all given that the insulation itself will be prone to freezing if it is water logged.
There are two main kinds of mineral wool, Glass Wool and Rock / Stone Wool. Either material is pretty interchangeable, although Glass Wool is slightly more efficient below 100ºC and Rock / Stone Wool is slightly more efficient above 100ºC. Quite a lot of specifications call for foil faced lagging to be used, and mineral fibre tends to be the most widely used as it is often the cheapest and most mechanically resilient. It is easily cut for making valves, corners and t joints so it can usually be cut to requirement on site.
Below is a video showing how the material can be installed. Again, we do not own the rights to this video and all credit goes to the creator. His videos are very good, we find that he explains things very well. I often recommend these videos to our customers as they are very useful. Its worth noting that since his is an American product it is faced with a white coating, but the method is exactly the same as one would use for the foil faced material more commonly used in the UK.
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Sager Foil Faced Fibreglass Pipe Insulation