Scuba diving fins, Flippers or Swimfins are worn on your feet just like a shoe or a boot. They are made of strong rubber or plastic and will help you swim like a fish. You can use Fins in many sports apart from scuba diving, such as surfing.
Scuba divers wear fins because human feet are generally too small (Mark Phelps excluded here) to actually help you maneuver under the water. We use the fins, as they are much bigger than our own feet. You don’t see fish with a huge body like humans with small fins, they wouldn’t get anywhere and also because we are using heavy equipment the fins help us swim like any other aquatic creature.
There are many types of fins you can use or purchase for example: Long fins or mono-fins are used by free divers. They use these because you don’t have to use so much energy to get to where you want to be and that is the main key for free divers because the more energy you use the less oxygen you are going to have, as free divers do not use breathing equipment. There are also very short fins and these are used by general swimmers or when surfing as it gives them a boost just in case they get caught in a tide or the current is too much for them.
Paddle fins are the most basic fins you can buy. They are simple stiff plastic or rubber blades which basically act as extensions for your feet to help you swim. Some paddle fins have groves and cuts to improve power and efficiency through the water. Paddle fins are designed just like Vented fins but you can wear boots and attach with a strap, paddle fins are like a shoe you just place your foot inside and place the plastic around your ankle and you’re ready to go for a swim.
Split fins are a normal pair of fins but with a big slice in the middle of the fin to help relieve the strain on your legs
Free diving fins are very long fins, they are just like paddle fins but just longer. You use them with a stiff leg motion and slowly kicking your legs. They are made of plastic, carbon fibre or fiberglass so they don’t weigh much
Mono-fins are typically used for free diving and are normally made of fiberglass or carbon fiber. Just imagine you are a mermaid or a merman. Both of your feet are in one big fin and with theses fins you would try and swim like a dolphin with a whole body movement.