You can make any curve a dynamic (hair) curve. When making curves dynamic keep in mind that hair stiffness is defined per CV and is dependant on the number of CVs in the simulating hair. By default this matches the number of CVs in the start curve. The Sample Density on the follicle can be used to scale this number. If the Sample Density is 2.0 then the simulating (and output curve) will have twice as many CVs and be half as stiff.

When applying Make Selected Curves Dynamic on a curve with only a few CVs (such as 4) the curve tends to be very stiff. You can lower the Stiffness, but if you want more detail in the output you can increase the Sample Density on the follicle. In terms of Stiffness, when there are many CVs on a curve (20 or more) the problem is usually achieving both more Stiffness and less Length Flex. The way you do this is by increasing the Iterations attribute on the hair system. In some cases you might want a floppy rope with many CVs that is not stretchy. For this you need higher Iterations and a Stiffness value that is very low (such as 0.001). In general you should use as few CVs as required, especially when stiffness is desired as this is more efficient.

For sample scenarios using dynamic curves, including images and workflows, see:

• Dynamic spline IK chain illustrated using a butterfly tail
• Stiffness Scale along curve and emit particles from curve example

To set the Make Curves Dynamic options

1. Select Hair > Make Selected Curves Dynamic> .

   The Make Curves Dynamic Options window appears. For descriptions of the options, see Hair > Make Selected Curves Dynamic.

2. Set the Make Curves Dynamic Options as desired.
3. Do one of the following:
   • Click Make Curves Dynamic to turn the selected curves into dynamic hair curves. The Make Curves Dynamic Options window closes.
   • Click Apply to turn the selected curves into dynamic hair curves. The Make Curves Dynamic Options window remains open.
   • Click Close to cancel the Make Selected Curves Dynamic operation and close the Make Curves Dynamic Options window.

To make a curve dynamic

1. Select the NURBS curves you want to make dynamic.
2. (Optional) Shift-select the surface or hair system to which you want to attach or assign the curve when it is made dynamic.
3. Select Hair > Make Selected Curves Dynamic.

   The selected curves are made dynamic hair curves.

   If you selected a hair system in addition to the curves, then the dynamic curves are assigned to that hair system.

   If you selected a surface in addition to the curves and the Attach Curves to Selected Surface option was on, then the dynamic curves attach to the selected surface.

4. (Optional) Customize your dynamic curves by modifying the attributes in their follicleShape nodes. For descriptions of these attributes, see follicleShape.
   Tip

   The Damp value can be used to relax oscillating curves on non-straight hair.