Kaipen is produced in northern Laos and is especially popular in the city of Luang Prabang. During the dry winter months (November to April), when the river level is at its lowest, the green algae called kai is gathered from the river bottom. It is washed and pounded thoroughly for several hours and then set into cubes. A hot broth of water, green and black olives and tamarind is then poured over it. Each cube is flattened on a plastic sheet and then placed on a flat reed mat. There, sesame seeds, and optionally dried sliced garlic, tomato and onion slices are sprinkled over it. The reed mats are then placed outside on a wood framed network to dry in the sun for at least 7 hours. The finished product resembles a large sheet of Japanese nori. The kaipen sheets are packed into plastic bags for resale.
Kaipen is rich in vitamins and minerals and tastes similar to nori but is slightly more sweet, bitter, and aromatic. Kai can be eaten by itself or used to flavor other foods. Flash-frying is the preferred method of preparation, after which it can be eaten like a potato chip.