Top Rated: Carinthia Defence 4 Sleeping Bag (8.5 / 10)
Category: Modular Sleeping Bag 3: Best 4 Season (Sub Zero) Bag and Extreme Outer
Scramble's Recommended Sleeping Bag System
The military modular system uses 2 bags: a lighter "patrol" bag (down to 0°C) and a medium-weight cold weather bag (down to -15°C) which combine for extreme cold (down to -30°C, but a total weight of nearly 3kg).
Scramble's recommended "modular" system uses 3 bags, is lighter and a little more flexible (better in hotter, arid conditions, yet still good down to around -25°C, the extreme combination weighing just over 2kg). This summary is for the sub zero outer bag: Sleeping Bag 3.
Review Summary
An extremely warm bag, exceptional in extended wet conditions, extremely robust and largely weather-proof, yet competitively light and surprisingly breathable. The Carinthia Defence 4, designed as a modular (host) sleeping bag, offers the user superb protection on its own (down to -15°C), and makes an almost bivi-like* protective outer for any lightweight down inner / liner sleeping bag options. When combined with Alpkit's Cloud Cover (hybrid down quilt and sleeping bag), the Defence 4 can extend its Comfort Limit reach down to -20°C, possibly to -25°C (though untested). Having used this bag now for many years, reservations that were present in early use quickly disappeared. On the surface its design seems lacking in technical sophistication, but in use one soon discovers that its sophistication lies in the choice and combination of materials used, their fabrication (and design in terms of how they're put together), its minimal points of failure and its robust and highly functional features.
A while back, military sleeping bags were tough but too heavy for weight conscious trekkers to seriously consider. The military got wise, lost some weight and went modular. No doubt using expertise gained in the development of their consumer range, in the Defence 4, Carinthia have created a synthetic bag that can compete with the top outdoor brands on weight, yet wins big when it comes to durability, robustness and weather protection.
An outstanding sleeping bag, and Scramble's top pick as our modular cold weather option (in the "4 Season Sub Zero Sleeping Bag and Extreme Outer" category).
* We don't recommend using this bag without some form of over-head shelter, as although it's practically waterproof, prolonged precipitation will overwhelm it.