Soymilk can be put in a stainless steel cup. If you fill it with freshly boiled hot soy milk, scalding to be exact, it's perfectly fine. Pour it directly into a thermos while it's still warm, and be sure to close the lid tightly. This creates an airtight, airless, high-temperature environment, and the bacteria inside will basically be killed, so you can rest assured. If you are drinking leftover warm soymilk, it is indeed easy to harbor bacteria. If you just leave it for a few hours, you don't have to worry too much. But if you want to let the soybean milk longer, you have to soak the thermos cup with boiling water to kill any bacteria that may be inside, and then pour in the soybean milk. It's not just soymilk that does this, but milk as well, and all kinds of soups and broths you think about serving in a thermos.

Expanded:

Soybean milk (Soybean Milk), a traditional Chinese Han drink, the earliest soybean milk was made by Liu An, King of Huainan in the Western Han Dynasty. Soybeans are ground, filtered and boiled in water. Soymilk is very nutritious and easy to digest and absorb. Unlike milk in the West, soymilk is a very Chinese national food, widely popular in the Chinese region.