Infra red mirror

[dr pepper]

Will an 'ordinary' piece of mirror glass reflect infra red.
I have put together a cloud detector using an infra red non contact thermometer chip mlx90614, I want to shield the thing from the weather.
Instead of using a germanium window I was wondering if I could aim the thermometer downwards into a mirror that reflects infra red from the sky into the sensor.
Or would the sensor just measure the temp of the mirror.
Common sense tells me because the light has to pass through the glass to get to the reflective layer it wont be any different than a layer of the same glass over the sensor.
Another idea I had was to buy a cheapo infra red thermometer gun & rob its plastic window over the sensor.

 

[FvM]

Bare metal can work as mirror for far IR, glass simply absorbs it. A thin polyethylene sheet makes a good far IR window.

 

[dr pepper]

Polyethyelene sheet is a good window, I might have some of that, would 1.5mm be Ok.

 

[FvM]

I have no transmittance data at hand, 1.5 mm should still transmit IR, 0.5 mm is probably better.

 

[BradtheRad]

There are solar cooker projects where you lay aluminum foil inside an upended umbrella. That means it reflects heat (infra-red).