I see.

You probably know already that the cooling of any object comes from three main heat fluxes: conduction, convection and radiation. In addition you have phase changes like evaporation that require large amount of latent heat.

Thin aluminium rescue blanket work mainly to reduce radiative losses by changing the surface properties of the object (more specifically the emissitivity).

When you are outdoors and have a clear sky the temperature of the sky (basically the temperature of the atmosphere is very low (point an IR thermometer at nighttime to a clear sky and you will read probably between -40 and -70 degrees C. 

In the lab however, your sky is the ceiling and walls of the lab. These are at the same temperature as the air and very close to the  outer surface of your object.

So the lab is not a good place to investigate the loss of heat by radiation.

Now you still can investigate the effect of convection (heat exchange with the air) and the effects of evaporation. But mind that some differences from a real-life situation and the lab will exist due to this lack of radiative cooling.

Alex