Hollow Collider

Need to create a Collider like a Cup (Cyllinder with one side not present) in which we can hold balls? Is it possible to create one?

You can create the mesh in any 3D modeling program. Mesh is one-sided, and you have to create the normals inward. Note that mesh colliders can only collide with each other if they are marked as ‘convex’. But if you do that, it will not hold any balls. So if you build a mesh, you will only be able to interact with simpler colliders like sphere colliders and box colliders.

Another way to approach this problem would be to build the colliders for the cup out of a number of box colliders (one per child game object) that would approximate the shape of the cup.