to keep the back straight, but you need not have a "rear" too broad. For cons, the cushion is effective and having back pain is a good sign, it means that straightens the spine. It is effective on a chair or a little hard desk chair. But there should be wider (or offer several widths) for use as a wheelchair, it is really too narrow. Still, well done the job for a reasonable price. As against the shipping costs are just delusional, I received in the mail as I thought that the fees were justified by DHL service. These charges are incomprehensible This cousin does not come when even on the other side of the world. I agreed to order it anyway because it was the best product I've found in a range of acceptable prices. I can recommend taking good account of its size as it forms an enveloping shell.