Unfortunately, bathroom ventilation fans often are set up so that they exhaust air to the space between ceiling joists, especially if the bath is located on a lower level toward the middle of the house.
The United States Postal Service defines a postcard as: rectangular, at least 3 1â2 inches (88.9 mm) high Ã 5 inches (127 mm) long Ã 0.007 inches (0.178 mm) thick and no more than 4 1â4 inches (108 mm) high Ã 6 inches (152.4 mm) long Ã 0.016 inches (0.406 mm) thick.
According to http://pe.usps.com/Archive/HTML/DMMA....htm#wp1002733 minimum thickness for a USPS postcard is 0.007 and maximum thickness is 0.016. Typical coated cover stock thickness is: 80 lb .008 100 lb .010 110 lb .011 120 lb .012 100 lb cover (270 gsm) is probably the most popular thickness for postcards.