Sea to Summit Altitude II - Womens regular
3-season sleeping bags are used in the 3 warmest seasons: spring, summer, and autumn. Therefore, they are the next warmest category of our sleeping bags, but be aware of the differences in how warm they are and match them to what you want to use the bag for.
Find the right sleeping bag here.
It's not at all insignificant whether you're going to sleep outside in March or June, which can vary widely in temperature. However, good qualities in your sleeping bag can greatly expand the range of when you can use it.
Good qualities typically involve being able to retain heat and being able to release heat if it gets too hot.
A down sleeping bag is more breathable and better at regulating heat than a synthetic bag. That means it naturally has a wider range of use.
But one of the good qualities of a down sleeping bag is also that it's much lighter. It can be packed much smaller than a comparable synthetic bag.
A sleeping bag naturally becomes warmer if it contains quality insulating materials.
Another good thing for retaining heat is a neck collar. It goes around the upper part of the body or neck. It keeps the heat down by the body so it doesn't rush up to the hole in the sleeping bag - where you breathe in fresh air.
Some 3-season sleeping bags also have extra insulation at the feet to make it easier to keep warm there. Some also have it around the hips.
The most advanced bags can have synthetic insulation where you lie, i.e., on your back, and down insulation at the top. This provides the advantage that where the weight of the body compresses the down, there is synthetic insulation that doesn't lose as much heat from that treatment.