Which of the following is necessary in order to use a vacuum cup to lift a porous material, such as a corrugated sheet for stacking?

Using a vacuum cup to lift a porous material, such as a corrugated sheet, requires specific characteristics to ensure effective adhesion. The correct choice emphasizes the importance of a cup with a very thin flexible lip. This design allows the lip to conform closely to the surface of the porous material, creating a better seal and preventing air from entering the space between the cup and the material. A thinner lip can also more easily bridge the gaps and irregularities found in porous surfaces, which is essential for maintaining the vacuum and ensuring the material can be lifted securely.

The flexibility of the lip plays a crucial role, as it permits the vacuum cup to adapt to the texture and profile of the materials being lifted. When a vacuum is applied, a tight seal is necessary to create the suction needed to lift the object. A very thin and flexible design can deform under pressure, enhancing the grip on more irregular surfaces typical of porous materials, hence facilitating effective handling and stacking.

The other choices suggest designs or methods that do not provide the necessary characteristics for optimizing the vacuum's effectiveness with porous materials. For instance, options suggesting rigid designs or inappropriate flow path sizes would likely result in inadequate sealing and vacuum retention, making it difficult to lift the material securely.