Add thickness to surface

I am trying to add some thickness to a surface. I did some searching and the most common suggestion is to use the OffsetSrf command.

I need the offset to be in both directions and also for the result to be a solid. It seems that I cannot do both at the same time. The “both directions” option is only available if I deselect the "solid’ option. Am I missing some trick?



I tried the OffsetSrf with a surface and Both Sides and Solid were able to be selected and set to “yes”. The procedure produce a closed polysurface. Can you post the model you’re having trouble with?


Keep in mind that Rhino is a Surface modeler.
Surfaces have no thickness.
To make a solid, you have to enclose the volume you want with Joined surfaces.
A simple case is a rectangular surfaces.You can use the OffserSrf command with the solid option set to Yes. Then Rhino offsets the surface AND draws the four side surfaces, then Joins them all together into a closed, solid polysurface.

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Based on testing V5:

OffsetSrf does not have the BothSides option for polysurfaces if Solid=Yes

OffsetSrf does have the BothSides option for polysurfaces if Solid=No

OffsetSrf does the the BothSides option for single surfaces whether Solid=No or Solid=Yes

@RaymondC Are you trying to add thickness to a polysurface rather than a single surface?

@davidcockey I created a new curve and sure enough you are correct…it is indeed possible to choose an offset that is on BothSides and ALSO results in a solid!

I guess I don’t understand the difference between a single surface and a polysurface?

A polysurface is two or more individual surfaces joined together at edges. For more on surfaces and polysurfaces see the User’s Guide > Working in 3D > Rhino Objects at

You can also use ExtrudeSrf with the “BothSides” and “Solid” options set to “yes” to accomplish this.

@asbeastos That was promising but this command is not working—probably for the same reason as the OffsetSrf command is not working. Evidently my surface is a polysurface and not a single surface although I have no clue what that means.

The attached file has the original curve and the surface created from the curve.

add thickness.3dm (49.9 KB)

Yeah, that’s a polysrf alright. You’ll find some benefit to spending some time with some of the learning docs and youtube videos available, and familiarizing yourself with 3d modeling terminology.

I don’t have any issues w/ OffsetSrf bothsides on your model.add thickness.3dm (201.5 KB)

Unless the input surface is planar, ExtrudeSrf with “BothSides” and “Solid” options set to “yes” will give a different result than OffsetSrf with “BothSides” and “Solid” options set to “yes”.

well…you did get a solid but it is not offset on both sides of the initial curve. :slight_smile:

I exploded the surface, used OffsetSrf (with BothSides=Yes and Solid=Yes) on all the individual surfaces, and then did a Boolean join. Seems to have worked.

right, there was no indication when i posted that that it wasn’t a planar surface we were dealing with.

1000 ways to skin a cat.

offset bothsides on the curve, connect the ends, then extrudecrvoffset_extrude.3dm (95.8 KB)

I like your idea of offsetting the curve first, turning it into a closed curve, and then extruding that closed curve. What command did you use to offset the curve?

The Offset command seems to be one and it even has an option to make the end caps. But I tried all the corner options and it seems to distort the curve in the corners.

That looks correct to me.
If your center curve radius is less than your offset distance, the inside corner will degenerate into a sharp corner.
Is that what you think is wrong?

Yea, you’re right. I was using a huge offset amount just for testing but when I use the real value, the inside corners don’t reach a point. All good. Thanks to all!

yeah, offset is what i used.

Since Rhino works on curves instead of meshes, a polysurface is a multipart surface. It is the equivalent to creating multiple meshes to form an object and then stitching them together to form a single mesh. With NURBS curves they form a polysurface. Poly meaning many not polygon. There are no polygons in a NURBS surface. Not sure if this helps clarify, but as a designer from the mesh modeling world, I had to grasp this as well.