Without question 'down' is the most efficient warmth per weight material you can get for insulation purposes, however it has one drawback. Once wet, is loses its fabulous properties and takes a while to dry. However these products all have excellent DWR skins these days and will take a small amount of damp weather before the water penetrates.

Primaloft is the synthetic alternative. Although heavier than down it is comparable to a 300 fleece and even if wet, will still have insulation properties. If wet it will still take time to dry, however you can use it some some warmth during this time. It is bulkier than 'dow'n to pack, but has other advantages as generally the insulation is put within more 'active ' clothing.

Whereas 'down' is more campwear or high altitude, 'Primaloft' is generally found in hardwearing outdoor clothing.

Both 'down' and Primaloft are warmer than a standard 300 fleece, without the packing bulk. Generally they are used in garments which are highly wind resistant too!

Look after any of these products by airing them and storing them at home 'un-stuffed' and they will last you for years.