What makes a flag an "all weather flag"?

An organization I am with is creating a display of American flags to honor Veterans for Memorial Day. We plan to have over 2000 4"x6" stick flags out from sunrise to sunset. However, we are increasingly worried about the chance of rain. The US Flag Code says that flags may not be flown in inclement weather, "except when an all weather flag is displayed" [ 4 USC Sec. 6(c) ]. But what makes a flag an "all weather flag"? Would the stick flags count as this? We really would like to be able to set up the display, but do not want to dishonor the national colors in doing so. Any suggestions?