There are two foam cores for Flow Straightening Devices in the kit. It is the builder's option to use these. I highly recommend using them. 1/16" sheeting will be used with polyurethane glue to sheet these foam cores. Once sheeted, sand the balsa flush to the cores and then glue on the leading edges and trailing edges. When dry, they can be sanded smooth with the skin. I use masking tape on the skin near the LE & TE while sanding to protect the soft 1/16" sheeting. I prefer to wait until later to final sand the LE & TE pieces.

Later, the FSD that rides atop the canopy will be cut and fitted using 1/16" ply templates included in the kit. For now, it can be left as seen in the pic.

I must apologize as I only have the single finish pic of this step.