Thank you for your question about Misty® Wasp & Hornet Killer IIb. This is a great question!
All aerosol cans need to contain empty space so they won't combust. This is true for everything from hairsprays to air fresheners to insecticides. The amount of space needed depends on the chemical formulation of the product. Misty® Wasp & Hornet Killer IIb 20 ounce cans contain 13-1/2 ounces of insecticide for your safety.
Keep Misty® Wasp & Hornet Killer IIb stored in places below 120°F, and away from sources of ignition. You can find more safety and first aid information in the Material Safety Data Sheet.
Hope this answers your question!