Hypermobility (colloquially known as being double-jointed) refers to the over-extension of joints beyond their normal range of motion. Insoles for Hypermobility need a deeper heel-cup than standard to prevent rearfoot motion and restrict eversion of the heel. Insoles with rearfoot postings are also useful, as they support the rearfoot and allow for a degree of customisation that's not achievable with a standard flat insole.