A door strip, also known as a door sweep or door bottom seal, is a device used to seal the gap at the bottom of a door. It is typically made of flexible material, such as rubber or vinyl, and is designed to prevent drafts, noise, dust, insects, and other unwanted elements from entering a room or building through the gap under the door.

Door strips come in various forms and designs, but they generally consist of a strip or sweep that is attached to the bottom of the door or the threshold. The strip is designed to create a tight seal when the door is closed, effectively blocking the passage of air, sound, and other elements.

Common types of door strips include:

1. Bottom-mounted door sweeps: These door strips are attached to the inside bottom edge of the door. They typically feature a flexible strip of material that extends downward to make contact with the floor or threshold.

2. Threshold seals: These door strips are installed on the threshold itself, creating a seal between the door and the floor. They are often used in conjunction with other door weatherstripping methods.

3. Brush strips: These door strips use densely packed bristles made of materials like nylon or horsehair to form a barrier. They provide a flexible seal while still allowing for ease of movement when opening and closing the door.

4. Compression strips: These door strips use compressible materials, such as foam or rubber, to create a tight seal when the door is closed. They are often adjustable to accommodate different door heights.

Door strips are relatively easy to install and can be a cost-effective solution for improving energy efficiency, reducing noise, and enhancing overall comfort. They are commonly used in residential homes, commercial buildings, and other spaces where effective insulation and weatherproofing are desired.