1. Observation surface: Generally, the surface of the pump with membrane is smooth and bright, while that without membrane is relatively rough, and the color may be dim.

2, feel texture: the film feels smooth, and there may be some uneven feelings without film.

3. Scrape the surface lightly: Scrape the surface lightly with nails. Those with films are generally not easy to scratch, and those without films are relatively easy to leave scratches.

4. Smell its smell: Under normal circumstances, there is a plastic smell in the film, but there is no obvious smell in the film.