How would I make a smooth crease in illustrator?

I was thinking some sort of mesh.

Answer

Not everything is a filter in Illustrator.

Starting with four lines:

• Blue = Waves


• Red = Frame



• Green = Spine

• Selecting the Waves > Menu Object > Blend > Make


• Menu Object > Blend > Blend options > Specified Steps = 20


• Selecting the Blend and the Spine > Menu Object > Blend > Replace Spine


• Menu Object > Blend > Expand


• Menu Object > Ungroup


• Selecting the new Waves and the Frame, get the Shape Builder Tool

and click where the shapes must be filled

• Fill them and delete the unused paths.

End: