There are two main purposes that a car sun screen can be used for, so choosing the best one will depend on why you need it. Some sunshades are used to protect the car itself, particularly the dashboard, steering wheel and upholstery. In order to choose the best car sun screen for this purpose, you will want to look for a solid unit that fits snugly against the inside of your front windshield. The other reason to get a sunshade is to protect the passengers, in which case you will want to look for units that filter out harmful ultraviolet (UV) light and stay in place even when the vehicle is moving at high speeds. Some sunshades also come with other options, such as retractable screens, that may fit your needs better.
The first category of car sun screens is made up of units meant to prevent the sun from damaging the interior of a car. Over time, the dashboard of a vehicle can fade or even crack due to sunlight, and a car sun screen can help prevent that. A solid unit that allows little or no light to pass should be chosen if you want to protect your dash and upholstery. Some car sun screens are cut specifically to fit one vehicle, while others have generic sizes that may not fit as well.
This type of car sun screen can also be used to regulate the temperature inside a vehicle on a hot day. If you want your car sun screen to help keep your vehicle cool while you are working or shopping, you may want to choose a reflective unit that also has insulating properties. By reflecting the sunlight and also forming an insulating barrier against the front windshield, this type of sunshade can result in a more comfortable internal temperature. The temperature may still become dangerously high though, so the use of a car sun screen does not make it safe to leave a pet or child in a vehicle unattended.
Car sun screens can also protect passengers from the sun. Suction cups and other similar means can be used to mount these sunshades to the interior surfaces of rear and side windows. Since the purpose of these shades is to protect passengers from ultraviolet rays, you should choose one that blocks this harmful radiation. Thin materials can make it easier to see through the window, but in order to work properly they should still be capable of blocking UVA and UVB light. You may also want to consider a retractable shade if you would like to leave the unit in place when it is not being used.