Hi everybody i am new to the backpacking light scene so please excuse me if the question i have for you more experienced hikers has an obvious answer that i have missed.I recently bought a cheap thin aluminium blanket thinking that if it does reflect body heat as the makers claim then if i put it on top of my sleep mat i will keep a lot warmer in my bagfor very little extra weight.If this turns out to be the case then my question is this---Why arent jackets lined with aluminium? depending on the thickness of the aluminium cloth used this could possibly do away with the need for fleeces or other mid layers completely.Thereby saving a lot of weight and space in rucksac.Anyway happy trekking to you all in the coming year.