Recently, I have heard so many good things about kelp and its nutritional benefits. First and foremost, is kelp a noddle or a plant or a string? What is kelp??? Kelp noodles are a sea vegetable in the form of an easy to eat raw noodle. Made of only kelp (a sea vegetable), sodium alginate (sodium salt extracted from a brown seaweed), and water, Kelp Noodles are fat-free, gluten-free, and very low in carbohydrates and calories.