Weatherstripping is the process of sealing openings such as doors, windows, and trunks from the elements, or the materials used to carry out such sealing process. The goal of weatherstripping is to prevent rain and water from entering by either blocking it outright or by blocking most of it and returning or rerouting it. A secondary goal of weatherstripping is to keep interior air in, thus saving energy with heating and air conditioning.

Automotive weatherstripping

Automobiles have weatherstripping on all openings between interior and exterior locations. Consider a standard four-door vehicle: the doors may require 20 ft (6 m) or more per door depending on the size of the opening. Windows will require upwards of 10 ft (3 m). Trunks require large amounts. Automotive weatherstripping has added difficulties that must be considered in the engineering of the parts. For example, the weatherstripping must function equally at keeping rain out when the vehicle is parked as when it is going at its maximum speed. Automotive weatherstripping must endure extreme temperatures (hot and cold); be resistant to automotive liquids such as oil, gasoline, and particularly windshield washer fluid; and must resist years of full sun exposure. Automobile designers do not have design continuity: all weather seals should appear the same. This is a problem as they will likely be manufactured of different materials by different manufacturers. Likely the most significant issue is that of noise. After paint quality, interior noise is the second most important factor in car quality as perceived by the consumer. When automobiles go over bumps the car flexes and vibrates causing relative motions between the relatively fixed body and movable parts like doors, windows, and sunroofs. This movement could allow water in the vehicle so the weatherstrip must compensate by filling the gap. What is worse, this relative movement can cause noises such as squeaks, rattles, and itches to be heard within the vehicle. Many of these issues can be alleviated if the weatherstrip manufacturer coats the weatherstrip with specialty coatings. These coatings bond to the weatherstrip, provide chemical and UV resistance, decrease the coefficient of friction reducing the force required to open or close doors, and reduce or eliminate noise associated with weatherstripping. Not all vehicles have coated weatherstripping which means the weatherstripping is much more likely to cause the above mentioned issues along with others such as premature failure of the paint causing rusting. This is a very surprising situation given that the cost of the coating is less than US$1 to US$3 per vehicle whereas the rubber and steel is tens of dollars (an entire car set of weatherstripping may be worth US$100 to US$300 in the total cost of the vehicle, which includes all labor and costs of the manufacturing equipment).

Automotive weatherstripping is commonly made of EPDM, TPE, TPO. Sunroof weatherstripping can also be made of silicone due to the extreme heat that parts on automobile roofs commonly encounter. Coatings for weatherstripping must adhere to all of these weatherstrip materials. Such coatings are commonly available (silicone is very difficult to adhere to, however at least one coating is commercially available for this purpose), however, like other paints and coatings, a large variety coatings are available and these have a large variety of coating performances. Poorly performing weatherstripping should be reported to the car dealership if the vehicle is under warranty as fixes may be known.

Weatherstripping in buildings

The materials used in weatherstripping are thresholds, a piece of material, either a sweep or a J-hook, to match the door to the threshold, and the actual weatherstripping itself.

Every exterior door, or door to an uninsulated room such as an attic, must be weatherstripped as required by building code

Building code

A building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of building codes are to protect public health, safety and general welfare as they relate to the...

s in various jurisdictions. Doors can usually be divided into private homes and commercial properties. Some of these doors receive custom weatherstripping at the factory.

Custom weatherstripping

Custom weatherstripping, contrary to pre-weatherstripped units, require much more time and is considered to be a specialized skill.

Weatherstrippers install a threshold, cut the door and install a sweep or J-hook to the bottom of the door, and nail spring-steel bronze into the door jamb to seal the gap.

Pre-weatherstripped doors

Pre-weatherstripped doors for private homes are usually made of fiberglass or a similar material and are shipped from the factory weatherstripped, hence the "pre-weatherstripped." The doors have a [kerf] in the door stop so that a foam, rubber, or vinyl strip can be placed inside for the door to rest against when closed. These doors also have the threshold — usually a molded piece of plastic — nailed to the frame in the factory. These units are not difficult to install and require very little skill for a trim carpenter where a weather-stripper is required for custom weatherstripping.