To soften the vermicelli, just soak it in warm water at a temperature of about 40 degrees for about 20 minutes. The reason why we don't use cold water and hot water to soak vermicelli is that cold water is difficult to boil vermicelli, while hot water may lead to the final cooked vermicelli being fragile.
The fans we usually buy are dry and hard. They can't be directly used for cooking, but should be soaked in water. Generally, we just soak it in warm water until it becomes soft.
The warm water we use to soak the fans is about 40 degrees. It's almost the same for about 20 minutes. Because the duration of soaking vermicelli will be affected by the ambient temperature and other factors at that time, there is no exact data on this duration.
Many people may be used to using cold water or hot water when soaking fans, but it is difficult to soak fans with cold water. It may take a long time, but they still can't completely soak fans. If you use hot water, it may cause the final cooked vermicelli to be fragile.