Every province along the seashore of Vietnam has the cói crafting. Cói is brocaded as sedge mat or smaller objects. Cói trees are mostly 1.6 – 1.8 m high. Cói are cut vertically and dried in three to four days.
Cói is murky white and is preserved in high places for gradual use later. The makers, after harvesting in September, usually weave for many months to use up all material. They weave the white cói. After weaving, the cói can be left in white or patterned, which is called flower sedge mat. Some sedge mats need to be dyed in threads before being colour-organized during weaving process, so that squares of pattern can be made.
Before weaving, the makers need to stretch threads with diameter of 1-1.5 mm thick and make them parallel to each other. The threads should be 25-30 cm higher from the ground, and 2 cm separate from each other. They are 4.5-5 m long so that two mats can be weaved continuously in order to save the time of stretching the threads. The width of the stretching area depends on the width of the mats. The threads are woven on a very long table. When weaving, there should be two people: one will sit below the stretched threads and flip the material, the other will weave the cói threads.
Beside the regular weaving, many areas use the technique of combining many smaller cói threads into the bigger threads that are 4-6 mm thick to weave thicker mat or rug. Because of the exporting market demand, many new models of cói sedge mats and rugs have been developed.
Alongside with brocading sedge mats, many makers also weave small objects such as purses, hats, boxes, coasters, bottle coats, and animals, etc. with vibrant colours. The purses are favored by lots of foreigners because they are quite soft, light, and easily organized. Some famous areas are Nga Son, Thanh Hoa; Kim Son, Ninh Binh; Hoi Village, Thai Binh.