1.

To make a balloon you will need a polystyrene bud.

The size I used: 35 mm x 27 mm. 

You'll find information about polystyrene and food safety here.

2.

You can use a small piece of sandpaper to round the pointy part slightly. You can round the top part too if it’s too flat.

3.

Use a florist wire* to make a tunnel in the bottom as shown in the photo. I inserted it to a depth of about 1.5 cm. Make sure you are inserting it straight. If the tunnel is not straight, the balloon will not be attached straight.

* I used size #20.