So, I recently heard about bolster in a way that makes sense.
At first I refused to consider the idea, but when it was pointed out the bolster absorbs the air space between braiding layers and helps prevent friction of the the braids from ruining the whip faster – I really like that idea.
To break it down, the bolster is a simple, thin sheet of leather – not braiding that wraps around your belly of the whip before you plait or braid the whip’s exterior. Then using sinew or such to hold it in place. The added benefit to this is that you now have a stiffer belly too.
I’m sure people do two if they do a double belly & there might be other’s who only do one regardless of doing a double belly style whip.
My spin on this is to add a set of tiny holes along the edge of one side to anchor your sinew and help you pull it tight. I have to imagine you would have to add matching holes to the other side to prevent it from sliding around – unless you’re using two vices or clamps to hold the core/belly in place?