w124 plastic bumper repair

[Smiley]

I need to repair a hole in the rear bumper. I plan to remove the bumper then fibre glass behind then a layer of filler to fill the hole - which is about 5 cm by 2cm. A few years ago I used Isopon on the front bumper and it has held up well albeit with a very small crack line where the filler meets the plastic. I guess this is because the filler has no flex in it.
Is there a better product to use?

 

[SilverSaloon]

yes use a proper bumper filler. halfords sell it. it flexes

Halfords | David's Bumper Filler 100ml

 

[Dieselman]

A better repair would be to plastic weld some similar material into the hole. Fibreglass wo't adhere to the plastic properly.