Please, download the zip file, open the zip file by double-clicking on it and copy/paste the script to your GIMP scripts folder (ie...C:\Program Files\GIMP-2.0\share\gimp\2.0\scripts). Refresh your scripts and you're ready to go. The script can be located under the Filters > Light and Shadow > Plastic Wrap All Layers...
Download plasticwrap.scm scrip from
hereThe lower number you use, the more plastic added. In my case I used 5. The effect won't be excellent, you will need to paint over the white segments as shown in my screenshort.
I hope this helps.