Glass Noodles and Fen Tiao: A Cook's Guide to Chinese Starch Noodles

Fen tiao, fen si, and the translucent noodles in your hot pot are not interchangeable. Here is how each one is made, which dishes it belongs in, and how to cook it without turning it into paste.

Walk into a Chinese supermarket and you will find shelves of translucent dried noodles that all look roughly alike. They behave nothing alike in the pan. Fen si, fen tiao, and the wide sweet potato starch sheets used in Sichuan cooking are made from different starches, and each starch gives a different chew, a different tolerance for liquid, and a different failure mode.

The Three Families

Nearly every Chinese starch noodle belongs to one of three families, named after the starch they are made from.

Mung bean starch (lü dou fen): produces thin, delicate, very translucent noodles that soak up cold dressings beautifully and turn mushy fast when boiled. These are true fen si, the noodles in cold sesame salads.
Sweet potato starch (hong shu fen): produces fen tiao, thicker, opaque, with a distinct chewy resistance that survives long braises. This is the noodle in pork and pickled cabbage stews and most hot pot platters.
Potato or cassava starch: the cheapest input, common in mass-market products; the chew is flatter and the noodles soften without ever becoming gel-like.

💡 Read the label, not the front of the bag — Packaging rarely distinguishes clearly between fen si and fen tiao. The ingredient list on the back almost always does: 绿豆淀粉 means mung bean, 红薯淀粉 means sweet potato, 马铃薯淀粉 means potato.

Soaking vs Boiling

The single most common mistake with these noodles is boiling them from dry. Almost all fen si and fen tiao benefit from a cold or warm soak first, which rehydrates them evenly and gives you control over the final texture.

Soak thin mung bean fen si in hot water for 5-8 minutes until just pliable, then drain. Add them to the dish at the very end.
Soak sweet potato fen tiao in warm water for 30-60 minutes, or cold water for several hours, until they bend without snapping. They then braise without disintegrating.
Never soak noodles destined for deep frying. Dry noodles puff instantly in hot oil, and soaked ones will not.

Matching the Noodle to the Dish

Think about how much liquid and time a dish involves before you choose the starch. A cold sesame salad has no cooking time at all, so it wants the thin mung bean noodle that hydrates in five minutes. A two-hour braise has plenty of both, so it wants sweet potato fen tiao that will still have bite at the end.

Cold dressed salads: thin mung bean fen si, soaked, never boiled.
Hot pot: sweet potato fen tiao, soaked, added two minutes before serving.
Braised stews, pork and pickled cabbage, chicken and mushroom: sweet potato fen tiao, added in the last fifteen minutes.
Stir-fried dishes such as ants climbing a tree: mung bean fen si, pre-soaked and drained, tossed quickly over high heat.
Soups with heavy broth, hot and sour soup: thin mung bean fen si, added off the heat.

The Water Temperature Matters More Than the Time

Starch noodles rarely go wrong because you soaked too long - they go wrong because you soaked in water that was too hot. Water at a rolling boil will gelatinise the outer layer while the core is still dry, and the result is a noodle that is simultaneously slimy outside and hard inside. Warm water and patience give you an even result every time.

If you have over-soaked a batch, do not throw it away. Rinse it in cold water to stop further hydration, drain thoroughly, toss it with a little oil, and give it a very fast pass through a hot wok. Recovered noodles work well in stir-fries even if they would no longer be right for a salad.