Through the 19th Century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate). The seaweeds used included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes.

Bongo kelp ash is rich in iodine and alkali. In great amount, kelp ash can be used in soap and glass production.

Kelp is also used frequently in seaweed fertiliser, especially in the Channel Islands, where it is known as vraic.

Kombu (Laminaria japonica and others), several Pacific species of kelp, is a very important ingredient in Japanese cuisine. Kombu is used to flavor broths and stews (especially dashi), as a savory garnish (tororo konbu) for rice and other dishes, as a vegetable, and a primary ingredient in popular snacks (such as tsukudani). Transparent sheets of kelp (oboro konbu) are used as an edible decorative wrapping for rice and other foods.

Kombu can be used to soften beans during cooking, and to help convert indigestible sugars and thus reduce flatulence.