How long do mylar balloons stay inflated?

Mylar balloons typically stay inflated for a longer duration than latex balloons, often lasting anywhere from several days to a few weeks, depending on factors like temperature and altitude. They are less porous than latex, which helps retain helium better. However, they will eventually deflate as helium slowly escapes through the material. Proper storage and keeping them away from heat sources can help prolong their inflation time.