Hi Anna, thanks for asking, it’s a good question which confuses a lot of people.

Ski boot sizes are made either on the 1/2 size or full size as the molds used to create the shells are very very expensive and this saves the companies some money. They then place in a thicker or thinner liner to get two sizes out of each shell as you had hypothesized.

So for example, I wear a size 10 shoe which equates to a size 28 ski boot. Some manufactures would have me buy a size 27.5 which is really a 27.5/28 and some would have me wear a size 28 as that is a 28/28.5. It depends upon the manufacturer but some 28/28.5’s don’t fit my feet. It also depends upon the last size as the narrower 99mm lasts do not fit my feet well as I have a wide foot so I need the larger shell size of 28/28.5 and others that use a 101 or 102mm last I can then fit the 27.5/28 shells. It is best to ask the manufacturer what their last size is and also what size the shells break on, either the 1/2 size or full size, and of course, try before you buy whenever possible.

One solution to this is to replace the footbeds you get with the boots as they are thin, flimsy, and provide no arch support. Inserting a thicker footbed will provide more foot comfort and arch support and also take up boot volume so that size 28.5 will now fit more like a 28 if that is what you are after as in my case.

I hope that this helps.