Relaxes UVs by pulling them out toward the edges of the texture area.
Make sure the object has UVs and a 
Material assigned to it.
You also need to have a texture projected onto a model in order to use the UV Pelt tool. This tool allows you to manually select the boundaries of the UVs where you want the surface to unwrap.
Using UV Pelt
Click the
UV Pelt tool on the Texture tab.
Select the edges that will form the boundary of the pelt.
Note
Press F to select the next edge in the direction indicated by the arrow. Press L to select a loop. Press ⇧ Shift + R to reverse the arrow direction.
Press Enter to unwrap your selection.
You can scale the pelt by increasing the Boundary Springs in the parameter editor. You can also use UV Edit to move the UVs.
For specific parameter help see the UV Pelt node help.