Rigged arms changing volume I have made a very simple model and rigged it with automatic weights. However, as you can see in the picture. When I bend the characters arm, it absoulutely changes the arm to this horrible thing.
(In case the image won't load: The characters arm, which is a cube, stretches thinly together at the beginning of it near the torso.)

I have tried sub-dividing the arm, it's completely covered in red in weight paint mode, but it's always imperfect in some way.

Please, is there a solution to this?
100% weight is not enough for ensuring a rigid stuck, check the deforming vertices: they surely have some weight relatively to another bone (shoulder, neck, head, ....). The vertices will move exactly with their bone if they're weighted to that bone ONLY (even if weight is not 100%).

So you have to remove unwanted weights.

Another method is to separate all pieces and parent them with the associated bone with the option Ctrl P - Bone.