The old-fashioned stiff fins
In the old days, everyone dived with stiff fins with hard and firm blades. These fins were made entirely of polycarbonate because they could not yet use silicone in the fins. They were real planks under water. Because the blades were very hard, much of the force you put in the fins was moved to the back of the side, so that the propulsion was not optimal. These fins are hardly sold anymore, because it is an outdated model.
Traditional all-round fin
The traditional all-round fin is generally chosen. It is a fin with a supple but firm blade in terms of bending. This means that the blade retains its shape, yet it is flexible enough to generate a powerful but supple propulsion. The more effective your stroke is, the more propulsion you have. This is especially useful if you are diving in an area where there is a lot of current. Diving fins used to have a rubber heel strap that you had to adjust every time. Nowadays the fins are secured with silicone rubber bungee straps. This makes it very easy to put on and take off your fins and it fits perfectly on your diving shoe.
This traditional fin is also perfect for travelling. Some fins are demountable and relatively light, making them easy to carry.