4. It is forbidden for a woman to place a cloth over her scarf, or for a
man [to use a cloth] to cover his hat from the rain (1), since people
generally don't wear these type of things as garments (2). If, however,
the intent is to prevent the rain from causing discomfort, it is
(1) Some authorities permit wearing a plastic rain hat over a regular hat,
if it won't fall off. This is only so provided people do not normally
remove it if the rain stops.
(2) If it cannot be considered part of one's garments, and its not jewelry,
then carrying it in the public domain is prohibited.
(3) The authorities permit wearing rubbers for the same reason (even those
who do not permit the use of plastic hat covers).