Think of kelp noodles as mainly a textural and bulk ingredient instead of a noodle. Kelp noodles are simply a sea vegetable processed into the shape of a noodle with the help of sodium alginate; they don't absorb much moisture, satiate or even have a distinctive flavor. They do add volume and crunch, however, and come in two distinct versions: a brown variety that works best when heated through and a translucent version you can serve warm or cold.
Transparent vs. Green
In addition to color, green kelp noodles differ from clear kelp noodles in texture. Green noodles have more pliability, and they taste best when heated. Clear, dried kelp noodles work in either cold or hot dishes. Green noodles have a slight briny taste, but not enough to discern when paired with a flavorful sauce or aromatic ingredient. Clear kelp noodles have a distinctive crispness; green kelp noodles have a bite best likened to a rubbery al dente that snaps.
"Cooking" doesn't accurately describe what goes on when you heat kelp noodles. Kelp noodles aren't heat-resistant, but they are somewhat resilient to its effects. You could simmer a bowl of kelp noodles for 5 minutes and another bowl for 30 minutes without a noticeable difference in texture or softness between them. You only need to rinse kelp noodles and add them to soups, stir-fries and sauces during the last 5 minutes of cooking, stirring occasionally to coat them and heat them thoroughly.
Clear kelp noodles are more suitable for chilled and room-temperature dishes because of their crunch, and their translucence adds a delicate feel to their appearance. A simple dressing, a few secondary ingredients and a few minutes of chill time in the refrigerator are all you need to turn a portion of clear noodles into a small side. For example, lightly dress clear kelp noodles in a rice-vinegar vinaigrette along with scallions, lemon juice, mirin and chili flakes. Try adding clear kelp noodles to an existing pasta or vegetable salad when you want a different type of crunchiness.
You may find you get best results from kelp noodles when you substitute them for regular noodles by volume. All the seasonings, sauce and ingredients are in place; you simply need to add the noodles at the same time as you would regular noddles in the recipe. Kelp noodles work better substituted in Asian dishes, such as pad thai, chicken with peanut sauce, lo mein and Szechuan noodles, than Italian-style pasta dishes.