Strengthening fibreglass doors.

[chrisgtx]

Does anyone have any good ideas how to strengthen 2 doors I’ve bought for my car?
I got them to save weight, they are only 5kg compared to my standard stripped doors weighing 17.5kg. But as you can imagine they are quite flimsy and I’d like to glue something lightweight into the door to give me a bit more crash protection.
I was thinking some repurposing sort of carbon fibre/fibreglass extrusion or something. In my original doors I glued in some aluminium box section from a roller door but that was quite heavy.
Any ideas?

[SystemOfAFrown]

In boats, stiffening ribs are formed either from wood which is then fibreglassed in (so both the wood and the fibreglass are structural), or with urethane foam or even a cardboard tube which is just used as a former for the fibreglass skin and adds minimal stiffness itself.

[GreenV8S]

If you want to stiffen the doors so they close better or don't flap around so much at speed, you could stiffen them quite a lot by adding fiberglass stiffeners as others have suggested. Neither the door nor any of these light weight stiffeners will give you the slightest protection in a crash. If you're after crash protection then you should be looking at side intrusion bars or air bags. Air bags are not usually a DIY option.

[hidetheelephants]

Any crash protection, anti-intrusion bars etc, would need to be stoutly attached to the rest of the car via the hinges and the door lock, otherwise it just means you get hit by the door rather than the car that hits it. I imagine that amount of steelwork would carry you towards the weight of the standard doors, if not over it.