Inflating a cylinder


Hello everyone,
I’m trying to recreate a cylinder being inflated inside a cavity and taking the cavity’s shape. I’ve tried using soft body tag (w/ gravity turned off) on the cylinder but keep getting funky results. Could you please share any tips how to do it?

Attached is a simplified setup of my scene. Originally it was modeled in Solidworks and imported in C4D R26. Also attached are screenshots of expected before and after results.
Thank you!

edit: I think I found a way to do it by using Collision object. I did few tests with an expanding cylinder colliding with a cube and it works fine (see the attached Collision.c4d file). Then I tried with a cylinder expanding inside a shorter tube but there seems to be a glitch and the diameter of the cylinder inside the tube is increased to the size of the ID of the tube and it’s not affected by the scaling animation. The rest of the cylinder scales as expected. (see Collision 2.c4d). Probably I’m missing something but I can’t find a solution to this issue.

Inflation.c4d (769.9 KB)
Collision.c4d (720.2 KB)
Collision 2.c4d (1.1 MB)


I’d do a point level animation on this one.
Start at the end frame.
Make tube editable … adjust inner points to match OD of the pipe
Inverse selection and adjust end points of tube and scale to match void
Assuming you selected 2 height segments for the tube … adjust those
for the void.

Now hit the record icon,
Move animation to frame 1 and adjust points to initial size of tube.
Hit record. Scrub back and forth to see what’s working, or not, and adjust.



@vid2k2 Thank you for the prompt response.
I really like your approach - it’s quite simple and effective. I did few tests and it works great. My workflow is that I export the objects to Keyshot as alembic file and render them as part of bigger scene which is already set and it would take me a lot of time to re-do it in C4D (with which I’m not that experienced).
The only setback I came across was that when adding a bevel deformer to the cylinder to add fillets to the edges and keying the offset (fillet radius) and got weird results when exported to alembic and imported in Keyshot as shown below.

Once again thank you for your help!


You can animate the radius of the caps to smooth them out.
Or, put the cylinder into a HyperNURB cage.

In my example, I just animated parameters of the cylinder
without any PLA as done before since there’s no pipe in the
middle of the bladder, etc,


Have a look at the Morphtag.
It is much like PLA animation, but you define two or more states that you can animate via slider.


Thank you guys.
I ended up using the Morphtag plus animating the cap radius of the cylinder and got exactly what I was expecting as a final result.
Your help was incredible.