I voted no difference
In 1984 two top Canadian anaesthesiologist did a series of experiments with twelve healthy volunteers, testing the thermal insulation properties of metallised plastic sheeting, (which is a 10 µm thick Mylar sheeting with thin aluminium coating.) Clear polyethylene sheeting and 100 per cent polyester thermal bed blanket.
The experiments were carried out on individual subjects sitting in a whole body calorimeter and covered first with a thermal bed blanket bag up to the neck. Then the three materials were tested, one at a time, over the original thermal bed blanket up to the neck. The temperature of the calorimeter was set at normal operating room temperature of 18° C. Metallised plastic sheeting provided the greatest reduction in sensible heat loss of all three materials tested.
Over all they found that, there was a 29.7% saving in body heat between having nothing (or just a blanket) covering you and being covered by the metallised plastic sheeting, there was a 20% saving when just covered in a thermal bed blanket, and a similar reading for just being covered in a clear plastic sheet (19.3%) . I take to mean that difference between the three is about 9.7% saving.
However, their findings concluded.
The reflective surface of the metallised plastic sheeting acts to reduce radiative (the difference between the incoming radiation energy and the outgoing radiation energy in a given climate system) heat loss from the body, while the very nature of the sheeting decreases convective heat losses by eliminating draughts.
So most of the saving was made by keeping the subjects out of the ever-present draughts.
Since then several others have also concluded that wrapping a body in clear plastic sheeting is just as efficient as Mylar, both, on paper at least, have testable benefits. However, a pre-warmed blanket provide as much protection over heat loss.
One problem that was found in the experiment was the amount of water vapour that condensed on the inside of the plastic materials (the anaesthesiologists recommended not using the Mylar and the plastic near any electrical equipment)
....... suffice to say the poll has more or less confirmed that I was right! (phew 
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