A New Undersuit


Cool Fix is a new player on the UK market. Part of a much larger Scandinavian group that has been in business for four decades, its field is protective clothing. Clients have traditionally been the military, including special forces, the emergency services, and commercial divers. Cool Fix is now offering its product line direct to recreational divers, branded under the name KLIMA Sport.

It's Thermodynamic jumpsuit uses a two-layer cloth construction, with special vertical channels between the layers. Once you are locked into your drysuit, there is normally nowhere for the perspiration to evaporate to. If the perspiration soaks the undersuit, it will quickly chill the diver. The Thermodynamic ensures that perspiration is kept away from the diver's body so that he or she remains dry and thereby conserves heat. Suits for recreational divers cannot generate heat. They can only slow heat loss. Air is a poor heat conductor and slows the transfer of heat from the diver's body towards the cooler water which is in contact with his drysuit. The special baffling in the Thermo traps air and slows head loss.

The bottle green Thermo is very easy to put on and features a full-length, centre, double-ended zip which can be used as a relief zipper if you are the right sex and have the right drysuit! The smooth outer surface makes it easy for the drysuit to slip over it. I tested the suit over bare skin and found the towel lining very comfortable and non-irritating.

The Thermodynamic is remarkably thin and supple, compared to my normal lightweight Thinsulate. I tested the Thermo over four dives and two days at Stoney Cove. I used my usual membrane dry suit, so the only insulation was provided by the Thermo.

I must admit I had misgivings. It looked too thin to be effective! So, I entered the water with some trepidation. Above the thermocline, the water was in the mid-60¡s and I was perfectly warm thoughout. I was observing fish and shooting pictures, so for much of the time I was moving very slowly, or was static and not generating much heat. We were finishing the dives after around 70 minutes because we were running low on air. I never got cold.

On a dive to 35m the water was in the mid-40¡s. I got cold quickly. Normally I would wear my lightweight Thinsulate, thermals and perhaps a cloth undersuit for these temperatures. However, I warmed up quickly at my safety stop and spent a further 40 minutes cruising the shallows.

Overall, I liked the Thermodynamic. Compared to Thinsulate, it is much less bulky and restrictive, making it easier and less tiring to don and doff or swim in. Unlike some woolly bears, it is comfortable on bare skin and does not leave a debris trail of fluff that can interfere with valves.

As claimed by the manufacturer, I stayed dry. Conditions were very favourable on the surface, so I did not test it for windchill.

I do not feel that the suit is suitable for cold water diving as a stand-alone undergarment under a membrane dive suit. For extremely cold water diving under a neoprene drysuit, which provides integral insulation, it might well be ideal. I use my drysuit for diving in the Med and the Red Sea and the Thermo would be perfect for my needs, especially as it is light and compact to travel with. For summer diving in the UK and much of Europe, it would also be excellent. I would use it in combination with other garments for cold water diving.

I have some minor personal criticisms. I would like hand-warmer pockets, and a place to store keys and change. That's about it, for quibbles. There are also none of the usual thumb and foot loops. I did not find this a problem, but others have commented on this. I tucked the legs into my socks, and held the wrist cuffs as I pulled my drysuit on. Anyway, thumb loops can breach seals.

I started out with very negative feelings about using such a seemingly thin suit in cold water. I expected to freeze. Appearances can be deceptive. My expectations were quite wrong.

From Cool Fix International Ltd, Knutsford, Cheshire, 01565 654906. Price £99 including p&p and VAT. Sizes: small to xxxl.


W e would like to emphasise that the limitation of the insulating properties of the garments are linked to the ability of the cloth to absorb perspiration. If the garment becomes soaked, you will have a cross-wire effect between the cold water outside the drysuit and the diver's body. Warmth will travel 28 times faster through water than through air. Any cloth will have a limited absorption capacity which, however, can be improved by the addition of a cotton garment on top of the undersuit when diving in extremely cold conditions.

As for the comments on missing pockets, this garment has been designed for technical divers who have never mentioned this aspect.

We do have in the product range a two-piece tracksuit in a slightly heavier cloth. This is not as tight-fitting as the one-piece suit that is tested here, but would, we would have thought, be the last word in thermals for recreational divers as they can also be used as leisure wear.

This particular suit was developed for the Scandinavian fire brigades. Their staff wear nothing but this clothing while on standby and when the alarm goes they simply put on their Goretex-lined Nomex protective suits.

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