I love making fireworks.I started making my own shells when i saw the prices of them online.You could save a lot of money making your own.You could find out on how to make arial shells here https://www.instructables.com/id/How-to-Make-Fireworks/

Step 1: Materials

For the glue you will need flour,pan,stove to cook on.
for the shell cardboard.

Step 2: Lets Start Making the Glue

Start by measuring out three parts of water by volume, and pour it in to the pot. Let the pot of water heat over the stove until it boils.

While the water is heating up, mix three parts of cold water with one part of flour by volume in a bowl. For instance if you boiled 150 ml of water, you must now mix 150 ml of water and 50 ml of flour. It must be mixed thoroughly until it looks like milk.

When the water is boiling in the pot, slowly add the mixture from the bowl into the pot and stir.

Stir until you have achieved the desired viscosity take the pot off the stove. If there are any lumps in the wheat paste at this point, pour it through a strainer to separate the lumps from the paste.
The paste is now finished and can be used as it is, however the paste is hot. To cool the paste rapidly, transfer it into a baking pan. The paste is then stored in a container with a lid. You will need to throw the paste away 1-2 days after you have made it, since it will start to smell bad.

Step 3: Now for the Shell

Cut your craft paper into thin strips and using a small paint brush, lay a strip of craft paper onto a newspaper and lightly apply the glue you made to it. Wrap the strip around the equator of the sphere and place another strip 90 degrees from the first. At this stage you can roll the sphere on a solid surface to effectively iron out the paper wrinkles. Add another strip to the exposed part of the sphere and then another at a 90 degree angle. You should now no longer see any of the exposed area of the cling wrap. Do this process 3 more times until you have achieve 4 layers of craft paper.

Using your thumbnail, locate the equator under the craft paper and using a razor blade gently cut along the equator line until the shell forms two hemispheres. Do not remove the craft paper from the foam ball, set them aside and let dry overnight. Once the halves have dried remove the inner foam ball.