When maki rolls are rolled up, the rice is placed on a sheet of dried and flattened algae called nori. Nori is dark green and can be purchased in the dried vegetable aisle at an Asian supermarket. If it’s at a regular supermarket, it will probably be available in the international foods aisle.
Nori is used in maki roll sushi and nigiri sushi. For maki rolls, the rice is spread on the nori, the ingredients of the roll are placed on the rice and the whole thing is rolled up and called makizushi. If the roll is rolled up inside-out, concealing the dark green color of the nori, it is called an uramaki roll. The most well-known variety of uramaki is the ubiquitous California Roll. The inside-out California Roll was invented in Los Angeles at a sushi bar in the 70s by a sushi chef who realized that Americans didn’t like seeing the dark green nori on the outside. When rolling makizushi, the nori may be used as a full sheet or cut in half.
Nori is used for nigiri rolls also. A very thin strip of nori is cut and wrapped around the fish and rice to hold them together.
Nori generally comes in packs of 10 and can cost anywhere from $3 to $30 depending on the brand and quality. Nori should be stored in a very dry location because it is very susceptible to moisture.
Nori generally has a rough side and a shiny side. Nori should always be placed shiny side down when rolling a maki roll because the rough side holds the rice down better.