I agree with Susie -- no more than 1 part shreds to 2 parts soap batter. I measure this by weight and this proportion has worked well so far.
I normally make a soap batch that is about 2200 grams total to fill one of my molds, so if I have 700 g of shreds, I would reduce the total amount of the soap batter to 2200 - 700 = 1500 g.
The batter needs to be at least at a "warm gravy" trace to keep the shreds suspended. By that time, the saponification is moving along nicely, so adding the shreds to batter at this point is like mixing grated apple into pancake batter that's rather rapidly turning into brownie dough. The more shreds to add and the faster moving the soap batter is, the more messy and awkward the process gets. The time I over-did the shreds thing and got myself into this kind of pickle, the finished soap was kind of crumbly where the shreds didn't get mixed in well with the new soap. :roll: