It's 180 degrees F for the reflective bubble insulation you show in the picture. Here is a shot of ours as well. The product is not designed or intended for a direct wrap around furnaces, chimneys, etc.
It can however be used around the furnace to reflect or radiate heat away from the insulation. The best way to see how close you can put the material for your specific application is to test some non-reflective material. Position the material where you want the foil insulation to go and allow the furnace to heat up and take heat measurement readings. The darker the material the better as it will absorb more heat.
The Class 1 / Classes A fire rating is for use with interior surfaces, insulation, drywall, and other materials used in building construction.
If you want a full breakdown of the testing and certifications for InfraStop bubble foil insulation please let me know and I can email it to you.