The Full Foot fin, or sometimes called closed heel or slipper style, is one that is worn barefoot and is much the same as putting on a regular slip-on shoe. Full foot fins are usually designated for warm water use such as in the tropics. This design offers no thermal insulation for the feet which is why it is also referred to as a warm water design.
With respect to sizing, the full foot heel does not have any adjustments so the range of feet that it fits is less than that of open heel fin styles. Those people with wider feet may also have issues with the full foot styling as the foot pockets are built to accommodate widths that are most common for the length of the foot of each size offered. People with high arches may find issue with the full foot design, due to the part of the pocket that covers the top of the foot which is, again, designed for the average foot. The pocket may cause stress by pushing downward making the fit uncomfortable.
Need more information? Then please check out our Snorkelling Fins Buying Guide.