AKA nightmare for pattern makers.
For a good reason. Not just because it is complicated – it is – but the perfect pattern is not enough, there is the leather factor – how this going to behave on the last? Will the crease line be too thick? Will it go the right spot? Can you sew it together without further issues? Factories make several prototypes and the very reason is to answer these questions and not messing up expensive raw materials.
The bellows tongue is not a design feature, more abut comfort and make the boots waterproof.

I am not going to share how to create a bellows pattern – if you don’t have the right book, you are looking for a long trial and error period – but show a few practical trick.

First of all, the crimping. The relevance of crimping is the accuracy, how it will follow the shape of the lacing. It is not impossible to make it straight and just trust the foot to shape it, but we prefer precision.

This is how it is going to look like.
to be continued…