Thanks guys! My sister got me birthday balloons, so many that I had to put most in the trunk and cut the big one off and put it in the back seat to get it home, then retie it onto the bunch. Some of the rubber balloons are already losing height, but the mylar ones are still Birthdaying in there.

Rubber balloons sagging in sag order (none have lost their plump yet, just not hanging as high):
yellow
white with color swirls
pearly blue
pearly red
purple with happy birthday tampo

Rubber balloons NOT sagging yet:
3x green with happy birthday tampo
pearly dark blue
red with tampo
pink with tampo

Weird, huh? Also, they're kinda undulating in the air conditioning stream.