A feet position guidance aid for formulating individually formed thermoplastic insoles, shoes or shoe sole structures. The feet position guidance aid is made of flexible material and its upper surface includes guiding places for feet for guiding the position of the feet. The feet position guidance aid includes a lifter, wherein the lifter is a rising structure arranged to lift up and support the toes of the feet so that feet are guided to a position suitable for formulating the individually formed thermoplastic insole. An insole customizing arrangement for formulating individually formed thermoplastic insoles is also described.