1. PolyUnwrapper UV Packer
This new packing method is very similar to the one that comes with the Unwrap Modifier in that it packs the Shells based on their bounding rectangles, but it does not rotate or mirror.
This packer uses Pixel units instead of UV units, so the Shells can be packed using Padding with pixel precision, which is good to avoid texture bleeding.
Rescale: Rescale the Shells to fit the Packing Area.
Padding: Is the distance, in pixels, between the Shell's bounding rectangles.
Fc: Specify the Scale Factor to Scale Up or Down the Shells.
Packing Area: Is the texture area (in pixels) where the Shells will be packed. You can get a packing area from a selection using the Dropper or you can specify an area manually by entering the Left, Right, Bottom and Top values in pixels.
Reset: Will reset the Packing Area to the values specified in the Render Tab.
The information about the Total Shells and the Packed Shells is shown underneath the Rescale checkbox.
PolyUnwrapper UV Packer does not automatically fill the "Shell's holes" with other Shells as the default Unwrap UVW does.
3. Pack UVs (3ds Max Default Packing Algorithm)
Performs a 3ds Max Pack UVs operation using "Recursive Packing" method.
Shift + Click: Pack UVs using "Linear Packing" method.
Ctrl + Click: Opens the 3ds Max Pack UVs Dialog.
Normalize, Fill Holes and Padding are the same as settings as 3ds Max Pack UVs Dialog.