The Sidas Volume Reducers 3mm are simply placed between the sole and the insole / footbed. This volume reduction means that shoes that are too wide or too large can be subsequently adjusted. The insole does not have an additional footbed. The correct size is adjusted to the existing insole using scissors.XS: 2 UK - 3 UK S: 4 UK - 5 UK M: 6 UK - 7 UK L: 8 UK - 9 UK XL: 10 UK - 11 UK XXL: 12 UK - 13 UK