Mobile Phone Cases, which are designed to attach to, support, or otherwise hold a mobile phone, are popular accessories for many phones, particularly mainstream smartphones. Case measures are based on the display inches (e.g. 5 inch display). There are different types:
Holsters are commonly used alone for devices that include rubberized padding, and/or are made of plastic and without exposed rigid corners. Heavy duty cases are designed to protect from drops and scratches.
A Standing case improves user experience, being specially recommended for multimedia, videos and audio. Folio case is a combination case and stand, and may include a keyboard (USB for OTG smartphones or bluetooth keyboard).
Skins and design covers can serve for protection and personalization. These are the result of the relatively "naked" designs produced by manufacturers such as Apple, where the metal and glass components of the device are exposed and vulnerable to damage. They are distinct from holsters, in allowing use of the device while in the case, but in many instances include a belt clip or other device giving it the functionality of a holster. They are made of hard plastic, rubber, or in the newer market adhesive-backed vinyl pieces. Vinyl skins can be ordered on many websites and come pre-cut to fit your cell phone or another electronic device. Vinyl material may be calendared or cast, with the latter being more expensive. Calendered vinyl is expected to only be used for short-mid duration (10 years) while cast vinyl is used on a more long term basis. Calendered vinyl also tends to shrink in the heat and can be shaped into any form (above 80 degrees Celsius) but might fade in direct sunlight.The today's standard of calendered films is almost as good as the cast vinyl. Cast vinyl avoids most problems, but costs up to 250% more. 3M has manufactured a cast vinyl product that they call "Controltac". This vinyl cover maintains a more glossy look and provides an air release channel that prevents bubbles during placement. The more popular is the cast vinyl because of the range of designs.
Customized phone cases use custom printing. Different companies have different methods of printing on cases, some utilize sublimation for printing on mobile phone cases, other methods include inkjet printed skins and Dye-Sublimation 3D printing methods.
Some phones have a replaceable cover. A release button on the cover lets it pop off to be replaced with the new cell cover. Phones that lack a replaceable cover can accept a slip on or snap on cover. These come in leather, vinyl, silicone, or hard plastic.
Functional cases can integrate an external battery, a USB, Bluetooth, WiFi keyboard and touchpad mouse in a similar way to tablets.
The article quoted from : https://en.wikipedia.org/wiki/Mobile_phone_accessories