I used to build my higher end sleep systems with a vertical chamber system that was split in two since full length chambers are prone to shifting, and offered my less expensive systems with horizontal chambers since they were much more efficient to build. However, over time, as I increased the chamber fill density the performance of the horizontal chambers easily caught up with the vertical chambers. In fact, I began to see advantages to the horizontal chambers. Not just build time and labor, but actual performance advantages. Before getting in for the night, a sleeper can intentionally shake the fill towards the center of the chambers so that there is maximum loft directly above them where it is needed the most, while limiting the fill along the back/sides where it is only needed to fill the gaps between the sleeper’s body and the sleeping pad. As long as the density is high enough to keep the fill from moving throughout the night, this can make more efficient use of a given amount of fill.