How to shop for a sleeping bag. Here are two great articles which gives an overview of the options and how to choose the perfect bag for your needs.
http://www.bigskyfishing.com/camping-gear/sleeping-bag-temperature-ratings.php
https://www.rei.com/learn/expert-advice/sleeping-bag-backpacking.html
Temperature rating is an attempt to describe what to expect and how to prepare for the weather and season. But in considering temperature rating one needs to know the conditions and factors that speaks to.
No matter the rating of any bag, an individual will have their own experience with it. Also, the rating is subject to change with things like humidity, wind, whether you are cold adapted, and what you ate for super, etc.
Wool is a Game Changer
The body actually becomes adapted to the cold with exposure to the cold. So a person may experience feeling cold at say 30 degrees the first few nights, and then later find they are perfectly comfortable at that same temperature and perhaps even at lower temps.
Wool sleeping bags facilitate this cold adaptation process. Wool is the only material that lets you breath inside….that is…crawl under the covers and breath. Synthetic materials would condense moisture and you would become colder, but wool releases the moisture and allows you to warm the air with your breath. This raises the temp. rating by up to 10 degree F. It also has the benefit of acting as a sleep enhancer by increasing melatonin production.
The Lucky Sheep™ wool sleeping bag is expandable and contractable. That means it can perform in a wide range of temperatures by the way you use it.
To further extend the cold performance, you can wear extra layers of insulated clothing. There is no zipper to confine the bag to one size. This bag expands. You can make your Rewilder 20 go to around 0 degrees Farenheit by wearing a merino base layer and then wool sweater.
On warm nights, you can open it up or let air in through the sides because you aren’t limited to all or none as in sleeping bags with traditional zippers.
And the Lucky Sheep™ sleeping bag unzips to become flat and can be used on a bed when you aren’t camping.