Just bought these cheap bubble balloons. They seemed to be pretty tight and thick, but it was not a problem to inflate them using lungs.
Important tip if you want to blow them by mouth: your first breath must be really strong and big. It will help you to overcome the tightness of balloon. Then blowing will not be a problem.
BTW, if you blow to pop them, you will have a huge bang. So I recommend to use earplugs. And sometimes balloons shred into small pieces which will hurt you. Be careful.
Important tip if you want to blow them by mouth: your first breath must be really strong and big. It will help you to overcome the tightness of balloon. Then blowing will not be a problem.
BTW, if you blow to pop them, you will have a huge bang. So I recommend to use earplugs. And sometimes balloons shred into small pieces which will hurt you. Be careful.