Bacpillow and the spine
The bacpillow is designed to support the spine.
This picture gives you an idea of how your spine sits on the bacpillow.
The bacpillow supports the spine
2 bacpillows
You can use two bacpillows, one on top of the other, if you are round shouldered.
Use 2 bacpillows if you are round shouldered
2 BACpillows can be used if your upper back is very rounded.