# One input was not extruded because it would have made an invalid surface

**URL:** <https://discourse.mcneel.com/t/one-input-was-not-extruded-because-it-would-have-made-an-invalid-surface/111086>\
**Category:** Rhino for Windows\
**Created:** [October 27, 2020, 11:32pm UTC](https://discourse.mcneel.com/t/one-input-was-not-extruded-because-it-would-have-made-an-invalid-surface/111086 "2020-10-27T23:32:41Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![rpatanav](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/rpatanav/32/256089_2.png) [@rpatanav](https://discourse.mcneel.com/u/rpatanav)\
**Post date:** [October 27, 2020, 11:32pm UTC](https://discourse.mcneel.com/t/one-input-was-not-extruded-because-it-would-have-made-an-invalid-surface/111086/1 "2020-10-27T23:32:42Z")

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I seem to cant extrude a curve into a surface. Works fine if I try to extrude as solid. However when I try to booleandifference, the output created a wierd ghosted solid.

 ![Screenshot (1)](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/8/c/e/8ce785ecc40dffe072528b0bf9f5d94b80c5914a.png) ![Screenshot (2)](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/0/f/b/0fbde9e2f9773523b8943cdb3944735c6a3e42d6.png)[curve.3dm](https://discourse.mcneel.com/uploads/short-url/me1Y35t80KTKrNMzf0A7WtEB2b6.3dm) (28.1 KB)

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**Author:** ![pascal](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/pascal/32/479395_2.png) [@pascal](https://discourse.mcneel.com/u/pascal)\
**Post date:** [October 27, 2020, 11:34pm UTC](https://discourse.mcneel.com/t/one-input-was-not-extruded-because-it-would-have-made-an-invalid-surface/111086/2 "2020-10-27T23:34:14Z")

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Hello - please post a Rhino file with the curve in it.

-Pascal

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<div class="post-metadata">

**Author:** ![rpatanav](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/rpatanav/32/256089_2.png) [@rpatanav](https://discourse.mcneel.com/u/rpatanav)\
**Post date:** [October 27, 2020, 11:38pm UTC](https://discourse.mcneel.com/t/one-input-was-not-extruded-because-it-would-have-made-an-invalid-surface/111086/3 "2020-10-27T23:38:57Z")

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done

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<div class="post-metadata">

**Author:** ![davidcockey](https://sea3.discourse-cdn.com/mcneel/user_avatar/discourse.mcneel.com/davidcockey/32/732604_2.png) [@davidcockey](https://discourse.mcneel.com/u/davidcockey)\
**Post date:** [October 28, 2020, 1:42am UTC](https://discourse.mcneel.com/t/one-input-was-not-extruded-because-it-would-have-made-an-invalid-surface/111086/4 "2020-10-28T01:42:35Z")

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One of the curves in the polycurve folds back on itself.

I found the problem by extruding the curve and using the Dir command to check normal directions. The normals for a closed surface should point out. In one portion of the extruded surface the normals point both directions which can only happen if there are multiple surfaces. Explode the surface and there are three surfaces, not one, in the problem area.

 ![Folded curve](https://global.discourse-cdn.com/mcneel/uploads/default/original/4X/3/2/9/3291cb8bef3a57ecc40f2340468c86f9fc4f231e.jpeg)