I find it interesting that a seat made entirely from carbon with a 200g twill layer each side (for prettiness) would be 20% stronger than a seat made entirely from carbon with a 200g twill layer on just the outside. I'd imagine a seat would have to be 3mm thick at least so the additional layer would do very little. (200g layer will add around 0.1mm thickness).
Are you using some sort of core material in the twin skin seats to add the strength?
sp-1 seats are made on 200gr twill carbon fiber as first layer, then satin 600 gr.
twin skin has a rear cover, ( just 3 layer ) but fixed with a structural resin/glue on the seat , add more rigidity, but at same time,keep low weight.
( sorry for my english, its hard to explain )