There seems to be no such answer to this question on Baidu.

A tailor or fashion designer who makes clothes should be able to answer your questions.

But I'll give you an answer from the fabric first.

Generally, the lining of coats is made of polyester taffeta fabric, and the fabric of polyester taffeta is basically polyester, which has no great elasticity. Once the elbow of your sleeve is bent. If it is as long as the outside fabric, it will be very simple.

First of all, the arm is inconvenient to bend,

Second, if you bend your arm too hard, the lining will tear like Arqie.

Therefore, the lining of coats and coats must be longer than the fabric.