For reference a bladder is also a pillow tank but a bladder may or may not be self supporting. The capability of a pillow tank with it's self supporting layout holds about 70% of what a rectangle would. IPI has labored with tank factories for just about 2 decades and https://www.facebook.com/permalink.php?story_fbid=pfbid0jhxLdXxnCyfkdydJGrWFvekywJn4e256moH1eEwKZDU5nNWNGCawT98nTvHm7Sq4l&id=61560512640678&__cft__[0]=AZVhoLB9A4ZOk1D-EYICsZY4nYUFM5N6W5yHcQ9MHW9DRgee6GC4DRyrloqQWs8nOgVDvkzyT3Etbt6d8irjMUDmJooHi574iOeZdLBeXjgVO-IkR7yfeMx4M_k4JCJQDtI1plepMrBzz4uZNcziGRzQI8uCmlbWsCZWPhQ38b5S3jFQaPCWuFeLKcsk_cLLeJBeqXshX1xQWhcMTUBmX3qu&__tn__=%2CO%2CP-R