Ramen noodles
Wheat noodles made with alkaline water (kansui), which makes them yellowish, firm and springy.
Fresh or dried ramen noodles are sold in Asian grocery stores, fresh ones often chilled or frozen. Supermarkets usually carry them only as instant noodles, whose noodle block works fine without the seasoning packet.
Substitute:
In a pinch, boil spaghetti in water with about a tablespoon of baking soda per litre. This comes close to the colour and bite, though the noodles stay less springy than real ramen.