Interior Door Trim Frame

I need to replace the fiberboard backing that is used as the base for my door trim.

I was thinking about using 3/16 or 1/4 plastic sheet.

Do you think that it would work?

I cant get fiberboard here in Germany and I need something that is rigid as fiberboard is not.

I dont really want to use acrylic, I can use PVC, HDPE, or acrylic.

http://www.tapplastics.com/shop/category.php?bid=24&PHPSESSID=200609272306392111669577

Are you wanting to customize this at any point or just replace it so it doesn't look so bad? I ask because I would just fiberglass the existing fiberboard and customize the panel.

I need to replace it since some of the blow molder connectors that secure the trim to the panel dont work anymore. The fiberboard which held them inplace broke. I'll try to take a pic to show you.

I couldnt find any 1/4 MDF here in Germany but they do have 3/16 and 1/4 fiberboard, the same crap that I have now. They also have 4mm~3/16 plexiglass sheets. Wouldnt those work?

Where were you looking?  A home depot type place?  Even here in the states those type of places don't carry 1/4" mdf, you have to go to a lumberyard.

Fiberboard just isn't very strong, obviously since yours broke, and plexi is just gonna be a pain to cut and its just unnecessarily expensive.  I get a full sheet of 1/4" mdf for about $13.  Half sheet of 1/4" plexi is about $50

Its hard enough to find a home depot style store here in Germany let alone a lumber yard.

The place I looked at had sheets of plexiglass that would be big enought for one door for $15. $30 for both is a steal here in Germany.