Perfectly round plastic balloon - Long stretchy neck, can be tied off like a latex balloon, heat sealed or tied off with a 260Q!
The trick to these is to actually allow them to stretch.You'll notice when inflating that they become quite hard, as if they are about to burst, but if you stop at about 35cm, hold the balloon for about a minute (you will actually feel the plastic become softer), and then continue to inflate to the full 45cm size.
You can actually take them even further with this method as they do stretch a lot if they have enough time too!
Also, when it hasn't had time to relax, stretch and soften, if you have inflated to a full stretch capacity and attempt to twist and pull the neck (putting more pressure onto the plastic) it will burst from the pressure. Treat these carefully when they are at their hardest. Wait until they soften up, they are much easier to handle when stretched and soft.Once already pre-stretched, you can re-use these balls over and over!