Experts agree that a housewrap should pass water vapor 5 to 10 times faster than the internal vapor barrier. Since most vapor barriers measure at 2 to 4 g/m2/24 hr., a minimum value of 10 to 40 g/m2/24 hr. is sufficient. This is the range for various types of 15 pound felts that have been in use for years. Typar HouseWrap is 3 to 4 times greater than this minimum value range.