I use a double layer of Thinsulate sandwiched between pertex. I've tried a down equivalent and found it to be only marginally warmer. It does however pack down smaller. The Thinsulate number occupies a 20 litre dry sack whereas the down was around half that. As John F mentioned, you need to keep the down dry where as many synthetics will insulate even when damp. At the end of the day cost and my somewhat twisted sense of ethics pushed me down the synthetic route. I won't push my own opinions here but you may want to research how the down is harvested and make your own decision.
Last edited by Dangerous Dan; 14-12-2009 at 22:18.
Evolution stinks, I want my tree back