Down skirts will be your warmest option. Down works well in most environments, though it does not provide much insulation once it gets wet.  Generally speaking, down does not breathe as well as synthetic insulation, so down skirts are best suited for light activity where you are unlikely to be putting off a lot of extra body heat.  All of our down garments contain only Responsible Down Standard (RDS) down, meaning that all the down and feathers used in our garments are ethically sourced. Synthetic insulated skirts (or vests and jackets!) are great for more active endeavors as they will breathe better than their down counterparts. For this reason, many of our styles that are designed specifically with active pursuits in mind use a synthetic insulation.  While synthetic insulation is not waterproof, it does perform better when damp compared to down.  If you live in a damp environment, we would recommend choosing a style that uses a synthetic insulation.  Several of our synthetic garments use Primaloft  Eco which is an insulation material made from recycled fibers.