Interior walls in sit-inside kayaks that go from one side of the kayak to the other. In plastic kayaks they are typically made of foam (occasionally of plastic). In fiberglass or Kevlar kayaks they are made of a composite material.
If a kayak capsizes, bulkheads make it easier to empty water out. Water will only fill the cockpit and not the bow and stern compartments.
The bulkheads not only create air compartments, for safety, but are also storage compartments to hold gear.
We recommend a double bulkheaded kayak for larger bodies of water. Areas like the Detroit River and the Great Lakes, where you may not be able to get to shore easily in the event of a capsize. Kayaks with bulkheads often have hull designs for water with potential wind and waves.
Periodically check bulkheads to confirm the seal is still in place. If a seal has failed it will need new sealant for the bulkhead to work properly.
It is good practice to dry the areas around the bulkheads after each paddle.
In a double bulkheaded kayak the bulkheads are behind the seat and in front of the foot braces. A single bulkheaded kayak will typically have only a bulkhead behind the seat. The bulkheads run from side to side.
Bulkheads in the bow and stern of a kayak make it difficult for the kayak to sink. They create air compartments and water will not fill the areas.
Some kayaks have hatches in the bow and/or stern but that does not necessarily mean there is a bulkhead.
Many recreational kayaks do not have bulkheads. These kayaks often have hull designs for calm, protected bodies of water like inland lakes and rivers. In the event of a capsize, the kayak will fill with water and the paddler will need to swim the kayak to shore and empty the water.
Flotation bags are air bags that will displace water. Flotation bags can be difficult to attach to the kayak and may move when really needed.
Some kayaks have foam pillars that run from front to back in the bow and/or stern. These pillars are structural pillar and will help some with flotation. We recommend using flotation bags with foam pillars.