Foot pronation is a tilting inward of the ankle. Slight pronation is a normal and necessary action of the foot during walking and running.
It becomes a problem when it is excessive.
Also, one foot may pronate more than the other. This will create imbalance in structure and function.
If you have excessive pronation of one or both feet you will need and benefit from custom-fitted and custom-made orthotics (arch supports).
In over thirty-three years of clinical practice I believe the best orthotics are flexible or semi-rigid.
Rigid orthotics will only create more damage to joints because the shock of walking will be transmitted to the knees, hips, sacroiliac and lumbar joints. They also prevent the feet from functioning as nature intended.
Make sure you don't settle for generic, off-the-shelf type of arch supports. Your feet are as different as your finger prints, so isn't it wise to be fitted for orthotics that are designed to support and meet your individual needs?