Ramen noodles
Wheat noodles made with alkaline water (kansui), which makes them yellowish, firm to the bite and springy.
Fresh or frozen ramen noodles are sold in Asian grocers, and dried ones in larger supermarkets. The noodle blocks from instant packs also work if you leave out the seasoning sachet.
Substitute:
Chinese egg noodles come closest, or spaghetti boiled in water with about a tablespoon of baking soda per litre. The baking soda gives them the colour and bite of ramen, though they never get quite as springy.