The extract coming from Laminaria Saccharina, a brown algae. According to manufacturer info, it's loaded with a bunch of good-for-the-skin things: alginates are polysaccharides (a big molecule from repeating sugar units) that are water-loving and can form a protective film on the skin. This means moisturizing, skin protecting and soothing magic properties.
The extract also contains another polysaccharide called laminarin, that has decongestant and lipid-reducing action that might be useful for combination, acne-prone skin types.
The third major type of actives in the Laminaria Saccharina Extract are phenolic compounds that have antioxidant and soothing properties. They can also trap heavy metal ions, and give sensitive skin some protection against polluted urban air.