Push Modifier

Modify panel > Make a selection. > Modifier List > Parametric Modifiers > Push

Make a selection. > Modifiers menu > Parametric Deformers > Push

Increasing amounts of push applied to an object

The Push modifier lets you "push" object vertices outward or inward along the average vertex normals. This produces an "inflation" effect that you can't otherwise obtain.

Interface

Push Value: Sets the distance in world units by which vertices are moved with respect to the object center. Use a positive value to move vertices outward, or a negative value to move vertices inward.