Yes, it will be polyethylene.

Others here are big enough and ugly enough to make their own decisions but personally I wouldn't touch that method with yours. Burning plastics is always a no-no in my book since some (notably vinyls) can produce hydrogen cyanide and most produce toxic/noxious fumes.

If you know up-front that it's polyethylene, doing the test is moot. If it isn't …

Hi Neil,

Sorry no.

Polyethlene when heated will produce an oily paraffin like stuff up to about 450 C ,above that black carbon deposits, various aldehydes, propane ,methylvinylketone and also several other things like acetic acid depending on temperature of course.

Also depending on how fast the temp. is reached which for a laser would be quite quickly.

More realistically just put a piece of the film in water with a small amount of detergent. Only polythene and polypropylene have a density less than water and will float. All others will sink.

I would rate the chances of the film being PVC as virtually zero and the chances of harming yourself by burning a small piece of PVC also as virtually zero unless you do something moronically stupid, of course.

PVC is nowhere as common as it used to be, partly because it is a difficult material to recycle compared to PET and polythene. When it was widely used e.g. in transparent bottles I can't remember ever reading of any cases of people being poisoned by fumes of burning PVC unless the fire took place in a confined space e.g. an aircraft interior.

There is a definite place for personal safety in all we do but it is sensible also to beware of the hysterical over reaction so often promoted by the media.

Oh dear – I do seem to have started a hare running here with an attempt to be helpful.

To be clear, I wasn't suggesting burning kilos of plastic, or tons in an incinerator. A piece of thin film about 2-3 mm square held on the point of a pin in a small flame is all that's needed and the risk from emissions is non-existent. Before IR spectroscopy became readily accessible, the flame test was a routine starting point for screening plastics. A version of it – the hot needle test is still sometimes used in heritage conservation, though largely superseded by spectroscopic methods for those who have access to them and can get suitable samples.