The PolyPlank foam bulkheads serve in two capacities.
Assume for the moment that your kayak project will have two storage areas accessed through two hatch covers. The 2" wide bulkheads (one just aft of the bow hatch and one forward of the aft hatch) act as "beams" to support the deck which has been weakened by cutting out the hatch and cockpit access openings. The bulkhead(s) divide the interior into compartments. Should your kayak overturn, water will be confined to the central cockpit area making a flushing of the water a lesser task than if entirely filled!
This material is tough: we have had 200 pound guys stomp on the flat face and stand on the 2" edge without damaging the material. Install the bulkhead(s) BEFORE permanently joining the deck to the hull.
The bulkheads are precut to fit particular locations (not necessarily at a station mold) to allow MOST paddlers the leg room required to engage the foot pedals.
The bulkheads are in pairs for the Resolute, Endeavour and True North; the double kayak Reliance requires a set of 3.
1) Bulkheads being installed in a kayak
2) Aft bulkhead being sealed to the hull
3) Installing a bow bulkhead in an Endeavour
4) View of aft bulkhead once kayak is closed up