A 7-8mm gel ball is a type of small, spherical gel bead that is often used in a variety of applications, such as in water guns, stress balls, and arts and crafts projects. They are made of a soft, pliable material that can be squished and molded, and are typically clear or translucent in color. Gel balls are known for their bouncy and water-absorbent properties, and are often used as a fun and unique alternative to traditional water balloons. A 7-8mm gel ball is slightly larger than a 6-7mm gel ball, and may have slightly different properties and characteristics. The specific size and properties of a 7-8mm gel ball will depend on the manufacturer and the materials used to make it.