The flat-head foundation brush is a common makeup tool used for applying and evenly spreading foundation, BB cream, CC cream, and other base makeup products. Here are detailed descriptions of its main features:

1. **Flat and Broad Brush Head Design**:
   - This type of brush typically has a large and flat brush head surface, which is beneficial for quickly covering a wide area of the face.
   - It is particularly suitable for full-face priming and can complete the foundation application in a short time.

2. **Even Application**:
   - The dense and firm bristles help the foundation to adhere better to the skin.
   - Ensures an even distribution of makeup, avoiding heavy and uneven appearances.

3. **Efficient and Economical**:
   - The flat-head foundation brush can effectively pick up and release the right amount of foundation product.
   - Compared to using fingers or a sponge, the brush can sometimes save more makeup, reducing waste.

4. **Enhanced Coverage**:
   - Using a gentle circular or sweeping motion, the flat-head foundation brush helps to improve the concealing effect of the foundation.
   - It makes the base makeup more refined and smooth, enhancing the overall makeup look.

5. **Precise Control**:
   - Although the overall area is large, the edges of the flat-head foundation brush are also suitable for detailed areas like the sides of the nose and the corners of the eyes.
   - It achieves a natural transition effect and is more precise and considerate in details.

Tips for using the flat-head foundation brush include:
- When using, take an appropriate amount of foundation and dot it on the face, then use the flat-head brush to gently spread it outwards from the center of the face.
- Gently circling helps the product better blend into the skin, avoiding visible lines.
- Regularly clean the brush to maintain hygiene and extend its lifespan, preventing bacterial growth.

The flat-head foundation brush is suitable for users who seek a natural, fitting, and seamless makeup base effect.