Fin fitment tips

Fins - the additional propulsion that we gain from these is significant and they also allow us to achieve greater distances and reach greater depths than we could without them.

Having said that, if they do not fit correctly (most common mistake is too loose), we will have a lack of power transfer (inefficiency) and worst case, a lost fin at depth!  This is a serious safety issue that must be avoided.

Size:
Make sure that your fins fit tightly with the desired sock-thickness required for your most common water temps.  As a rule of thumb... if you can get them on dry... they are too loose.  So trying them on in a store is not always the best way, unless they have a bathtub or will hose you down first.

I bought fins that were a size and a half too large, so that I could fit 5-6mm socks inside for single-digit temp cold water diving.

I prefer at minimum to use a thin 2mm bootie, just to avoid chafing / blisters and also allows for diving in cooler waters / cold at depth for shorter periods of time and still retains good power transfer.

Those living in a diving paradise (Egypt, Caribbean, Thailand, etc.) may opt for no socks at all for simplicity and better power transfer.

Here is a very interesting looking sock that I have yet to try, but is on my list: http://www.canamuwhgear.com/product-p/bootie-argos.htm

Fin-keepers:
I find these essential and tremendously helpful in both keeping the fin secure and aiding in power transfer.  It makes the fin both safer and more efficient.

I choose these thick ones which are far superior to the thin ones commonly available.

Finserts:
I found that my UWH fins were softening up over time and many people experience their foot pockets on freedive fins getting tired with age.  A great old UWH trick is to make a "finsert", which is really just a polypropylene orthotic.

I bought a 12"x 24" x 3/32" thick sheet of polypropylene from Amazon.com for $8 (plus $10 shipping to Canada) and this was enough for 6 finserts.

I took the insole out of a pair of shoes and traced it and then cut it out with some tin snips (overkill) and then edged them with electrical tape (freedivers tape) so that the edges didn't abrade the rubber foot pockets.

They stiffen up the footpockets and help with power transfer.  If you don't have much space in your footpockets, you can use 1/16" thick.

The advantage with these is that you can double the thickness with a second pair if you want to use a thinner sock with your fins.

Something like this is now commercially available from Mares and available at diveinn.com and canamuwhgear.com as well, but I have no experience with them.