There are three common types of airsoft grenades, outside of pyrotechnic grenades, that you can use in regular airsoft games. If you are interested in those, definitely check out our more in-depth Airsoft Grenade overview.
The first common type is the Gas Grenade, easy to refill with your standard green gas and BBs, it releases a storm of BBs around the impact site. They are also the most accepted grenades depending on the field's rules.
The airsoft Sound Grenade can also be seen on the fields. These do not necessarily throw BBs unless you decide to add them but instead deliver a loud bang. Filling them with gas and a new blast cap, it is a quickly rechargeable and reliable grenade that comes in a compact format.
Finally, the Mechanical Grenade comes as a less impressive and less robust, yet viable solution for you to take on the field. It is cheap, doesn't need any gas as it works solely on spring power and is still capable of delivering BBs in a wide radius around it.