Actually, Tobus, the standard rain cape isn't any heavier than a good backpacking poncho - not the 'emergency' ponchos that come in a little pocket/pouch, but a good one that could be used as a ground cloth or emergency shelter. I have one with grommets on the corners that rolls up into a 3" dia. cylinder about 6" long. Fits quite nicely in my daypack and weighs less than my full water bottle. I agree that a wool Inverness cape or a normal overcoat is too much for regular hiking.

I've been in a downpour at a Highland Games that absolutely drenched folks that weren't prepared (guess who stayed - relatively - dry). It's kinda funny to see people walking around in the rain with little rivulets running off of each pleat of a soaked kilt!