I have a cheap infrared thermometer that works with a fixed emissivity of 0.95. My understanding is that the thermometer measures the amount of thermal radiation at some wavelength (range) and estimates the surface temperature from that.
What I don't understand is why that temperature is (more or less) accurate for different materials. For example, white paper has an emissivity around 0.7 and rubber has an emissivity around 0.95. I couldn't find out which wavelength my thermometer uses, so I'm guessing it's around 50 micrometers (mid infrared). Then I would expect the thermometer to display temperature differences >50° between paper and rubber for the same real surface temperature:
But in fact I get very similar measurements. (Less than 5°C differences between all materials I could find)