Inflate an Object inside a cage

I’m trying to inflate the highlighted portion to warp around the structure. Similar to playdough being mushed through a mold or a balloon being blown up in a cage. I have been searching options with no success. Any ideas or tips of how I could do this within grasshopper or rhino? The goal would be to have blobs forming from the warps created.

Hi Tyler, this can be done with Kangaroo. Careful on the subdivision of the object inside. It might take a lot of time…

For my simple case I used a SubD Sphere which I created in Rhino. The Solid for the collision is also created in Rhino.

21_02_26_inflate_collision.3dm (118.0 KB) (19.2 KB)


Caged (13.6 KB)

Here’s another version using meshes no subd. It’s also pretty slow. I made this a while ago and rendered the result:


Nice render!
I think I see a way to make this faster…



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This should be a bit quicker than using the solidpt collide-
(added a new collider goal between static pipes and points)
Caged (20.8 KB)


I don’t want to derail this thread much, but here is latest on that Anish Kapoor sculpture at 56 Leonard.

The individual panel pieces are fabricated to fit so tightly together, the joints aren’t noticeable. The fabrication technique was invented because the process of welding and polishing the joints for Cloudgate in Chicago was lengthy and tedious.

Is this faster because you’re using pipes for the collision?

My example above might be slow because of the high subdivision…

“Is this faster because you’re using pipes for the collision?”

Exactly - checking for collision with a pipe is much quicker than with a mesh.

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Except it’s been half-built for a very long time now. Not sure why they haven’t been back to complete it.

Yeah, I’ve been curious about why they paused as well. I hope they didn’t begin to have trouble with the assembly system.

You can try InflateMesh

inflate (18.3 KB)


I would assume it has all been fabricated because to get the joints to mate perfectly they would need to shop finish the complete sculpture.

Edit: Thinking about it more, I bet the reason is more practical. They don’t want to restart the install until there is an appropriate time on the horizon for a ceremony (post-COVID) to unveil the completed sculpture.

As comical as this is, what is the best way to prevent an exit, other than bars on windows? I tried using an anchor goal but I suppose it’s not that simple since the original point isn’t being moved.

blob exit

anchor inflation (25.3 KB)


Hey Weston, the anchor you set doesn’t do anything because it doesn’t share a location with the mesh.

The pipes your balloon is supposed to collide with are very thin compared to the mesh division. The mesh sphere needs to be refined for a good collision.

To prevent it from sliding out, you can add another object and keep the vertices out of that with a Solid Point collision goal.

I think the normal solver does a better job than the bouncy solver…

anchor inflation (36.1 KB)

I played around some more and after cleaning up your curves we can also use the Solid Point collision goal instead of the custom goal. Not sure if this improves the overall speed of the simulation. (905.8 KB)


@martinsiegrist Thanks Martin, that is incredibly helpful!

Not sure about the speed either, my laptop only runs on slow af when inflating…

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