My idea is that you should make resin that can be used to make functional living hinges. The amount of possibilities this opens up for useful items that people can create on their Form 1 is insane!
Related to this, if people have links to professional printing services / resins / etc that can do living hinges, it could help the conversation on whether this will eventually be feasible on the Form 1 
Injection molding living hinges are strong because the polymer molecules become aligned by the injection process. Thus 3D printed living hinges will almost certainly require a more robust design and be less durable than injection molded parts.
For 3D printed living hinges, laser sintered nylon (e.g. duraform) is probably the best choice, but even they will tend to break with repeated use. (e.g. http://www.lasersintering.com/ ). Living hinges made with Objet resins seem to be even less durable, but they can make very nice looking prototypes ( http://www.stratasys.com/applications/functional-prototyping/living-hinges ).
Any material CAN be used as a living hinge… It just depends upon how many degrees of bend are necessary and the thickness/length ratio needed (for instance a living hinge made of granite would probably have to be miles long per mm of thickness…)
I don’t know if there is a simple material property that measures suitability for living hinges.
Here are pictures of our first attempt at making a living hinge - promising but not great… It seems very fragile and is starting to break after flexing it only a few times, but definitely flexible. Thickening hinge would likely make it stronger but less flexible. Perhaps generous fillets to reduce stress concentration would be helpful. It was made in the open configuration, so that both flaps could be supported.
Hi Crispin,
Thank you so much for trying that out! Can I ask, was that done on a Form 1 or on some other 3D printer? Also, was it made using a geometry like in the picture I have attached here?
I am extremely excited by this! I actually only need the hinges to bend once into position for the design I was wanting to try out, and so if it is feasible on the Form 1 that will be a huge help to me.
Again, thank you very much for following up on this 
Hi Stephen,
It was done on the Form 1. If you only need to bend it once, I think it would be fine. The design was a little different (just pulled it from GrabCAD) so I have attached dimensions here. I like your design - it builds in generous fillets as part of the design, not an afterthought.
Well, I wish I could take credit for it but the dimensions were recommendations from ProtoMold :-). Thank you for sharing yours, this has been extremely helpful and I absolutely cannot wait for my Form 1 to arrive so I can try it out myself
Hi All! I just have made 5 test objects with living hinges, and they work well, so far (haven´t been bending them very often yet). First I printed two 0.2 mm layers of soft PLA, and on this soft 0.4 mm layer two objects of normal PLA, 5 mm thick. Between them I had gaps from 0.2 up to 0.5 mm, and on either sides of the gap a 45 degree slant. So you can bend them 90 degrees to one side, and 180 degrees to the other. With all these gap distances it works well. I guess, 0.5 mm lasts longer, but 0.2 mm provides less play under load. For soft PLA, a printer with the drive right before the nozzle is better, and a structurized plate (it sticks).
Best Regards, Elmue