The temperature at which a "standard woman" (or cold sleeper) can sleep comfortably in a relaxed position.

Crucial for cold nights to trap heat escaping from your head.

Tapered for a body-hugging fit to maximize warmth and minimize weight. Best for backpacking.

A compromise that offers more wiggle room than a mummy bag while remaining more heat-efficient than a rectangular one. 4. Key Features to Look For

Offers the best warmth-to-weight ratio and is highly compressible, making it ideal for backpacking. However, it is more expensive and loses its insulating properties if it gets wet, though "hydrophobic down" treatments can mitigate this.

The temperature at which a "standard man" (or warm sleeper) can sleep for eight hours in a curled position.