An aluminum self-opening and retracting three-fold umbrella typically has the following characteristics:

1. Material: The umbrella frame and shaft are made of lightweight aluminum, which makes it easy to carry around.

2. Folding mechanism: The umbrella can be folded into three sections, making it compact and easy to store in a bag or backpack.
   

3. Self-opening and retracting mechanism: The umbrella can be opened and closed with the push of a button, making it convenient to use when getting in and out of a car or building.

4. Canopy: The canopy of the umbrella is made of waterproof and windproof fabric, which helps to keep you dry and protected from the elements.

5. Size: The size of the umbrella canopy varies, but it is typically large enough to provide coverage for one or two people.

6. Handle: The handle of the umbrella is usually made of rubber or plastic, which provides a comfortable grip and prevents the umbrella from slipping out of your hand.

Overall, an aluminum self-opening and retracting three-fold umbrella is a convenient and practical accessory that can help to keep you dry and protected from the rain and wind.