Of course there must be some (lower) limit to how light things can go. It seems insulated clothing & sleeping bags are about to experience one of those quantum falls. Introducing Aerogel & Graphene: http://futurism.com/jackets-withstand-liquid-nitrogen-made-using-solid-material-thats-99-8-air/ You can already buy Aerogel blanket insulation eg here: http://www.buyaerogel.com/product-category/blankets/ Could be the ‘must do’ for DIYprojects? It will probably have to get a little cheaper first too! Unless I a misreading the data sheet it may never be light enough for our purposes though (or breathable). Spaceloft 5mm blaket’s quoted density is 0.15 g cm-3 (2.45 oz/69 g per square foot) which would be 621 grams per square yard – much heavier than competing ultralight hiking insulation. I may be sticking to my 900 fill power down sleeping bag a little longer yet!