For reference a bladder could also be a pillow tank but a bladder might or might not be self supporting. The capability of a pillow tank with It is really self supporting design retains about 70% of what a rectangle would. IPI has worked with tank factories for nearly 2 https://www.facebook.com/permalink.php?story_fbid=pfbid02E3TWTUy9Eu9quy6Lm13V7svM7cQfxNrgoCRvWpjv2eCmBT6BkFSQmtuQ3qp3vRXBl&id=61560512640678&__cft__[0]=AZXfDEcRapk5Ie2ZJu5EFiIBXOx7cuJYzrDAAVwDjicYHia3BrrEqzUUsCUwkD9McvxjMPjRzogCOVasvZhHyY2GR3XDG6hc347XAz5IEqAFzG6u0LC2UHo6pcxMGgJma1EvPzC9OMRz_0brnjTEAToCbJ8anYTmKca7n9USiOERbVTU2DcDea8cYwAKOAiW9A1fEJJ9gVfzwCGqNcuMJvao&__tn__=%2CO%2CP-R