Our synthetic sleeping bag range here at Gear-Zone includes 4 Season cold weather classics like the Mammut Ajungilak Denali, designed for the harshest of climates.
With an extreme temperature low of -49°c, the Denali is a combination of Shelter TX and Endurance TX fabrics, with Body Zone insulation MTI 11 filling for Polar and expedition use. Or there's the Mammut Tyin series and the women's-specific Kira Spring and Winter to choose from too.
From Mountain Hardwear there's the Lamina range, and from Snugpak we've got the Softie Chrysalis with its amazing temperature control.