Note
How long does a mylar helium balloon last? About 57 days. I came home from the CMO champs with one of the balloons from the Trail-O, which has been in my bedoom ever since. About a week ago it was not able to lift all of its string, so I started clipping the string down shorter, until yesterday I snipped it down to nothing. It disappeared overnight, and I had to wander around the house to find it hiding behind a door. It initially seemed like it was able to still float, but some experimenting showed that it couldn't really stay off the floor. It worked better in cooler rooms, so I took it outdoors where it was able to rise, and I screwed up and it drifted away. I briefly felt like a jerk, but once it cooled to ambient temperature, it came back down on the other side of the house. It has been returned to my bedroom, just barely touching the floor for now.