I've used both down and synthetic sleeping bags, and the synthetic sleeping bag that gets typically sold in regular outdoor stores tends to be heavier, more bulky, and comfortable in a (much) smaller temperature range. Are there other synthetic materials that share the advantages of down sleeping bags but that are not based on animal products?
There are higher end synthetics available that are much better than the regular poly fill stuff you see in average bags.
The two main companies for better performing synthetic insulation are Climashield and Primaloft. Both offer several levels for insulation and some differing technical aspects. Many brands even the more common ones you find in regular outdoor stores probably offer bags with either of these insulation you just have to look for the tags. They will usually have a separate tag that says what insulation it is and some of the marketing and technical details.
Brands to look for that offer these insulations. That I know can be found in chain outdoor shops in the US, Canada, and Parts of Europe like REI, MEC, Cotswolds, and Unterwegs. All of these stores also offer international shipping for online orders as far as I know.
- The North Face
- Mountain Hardware
- Mountain Equipment
I'm fond of Climashield personally and have two quilts, an older one with the original Climashield Combat and just this week received a custom made quilt with Climashield Apex 200.
To help you find a perfect match a somewhat more specific set of requirements would be needed, but these should be okay for even low temperatures and should be pretty down like.
Heavier ones (5-6 lbs; 2–3 kg):
- Big Agnes Whiskey Park - 0 degrees Fahrenheit / -18 degrees Celsius
- Marmot Trestles - 0 degrees Fahrenheit / -18 degrees Celsius
Lighter ones (3-4 lbs; 1–2 kg):