The shape of the real resting bag is to personal preference. The general selections are the normal rectangular form, the conical form, or the mommy bag. Some individuals might not such as the feel of sleeping in a regular rectangular shaped bag, favoring the closeness of a tapered one, whereas others may really feel too claustrophobic.
There are primarily two types of sleeping bags. One is the mommy bag and the various other is the "traditional" rectangle-shaped resting bag. Currently mind you, ain't nothing incorrect with old school in any way. It might be your preference once you uncover just what it's like verses the mommy bag.
Semi-Rectangular: I call this the cross. This backpacking bag is rectangle-shaped ahead and afterwards slenders along towards the feet. With this type, you obtain added space, but not as much weight as a true rectangular resting bag. For those who are claustrophobic, like me; we can reach sleep a little better inside a bag with added room in it and still have some benefit from the form.