Trendy magazines shout about carbon offsets: the small amount of money they pay to developing countries to assuage the guilt of sending journalists long distances in planes.
I sometimes think we forget that carbon-fibre is a man-made material that revolutionised jet engines, and made it possible to build such things as the fuel-efficient turbo-fans that power heavyweight airliners.
The high potential strength of carbon-fibre was first realised in 1963 in a process established at the Royal Aircraft Establishment in Farnborough, and a licence was granted to Roll-Royce enabled it to develop the RB-211 engine that saw it break into the US market.
Later versions of carbon-fibre have been used to reinforce polymers, combining impeccable corrosion resistance and high strength with light weight. Notably for regulator use, carbon has a thermal conductivity greater than any commonly used metal and, of course, its light weight will be welcomed by any diver packing for a flight.

First Stage
The MR42T first stage looks very similar to other small first stages such as those fitted to the Proton Metal and Abyss 42. The T stands for trimaterial, because the manufacturer uses brass and a soft polyurethane as well as a heavy-duty polyurethane.
There are two high-pressure and four medium-pressure ports, arranged at convenient angles to allow for uncluttered hose routes. What sets this first stage apart is its finish, in a hard-wearing physical vapour deposition (PVD) coating said to give it resistance to external knocks and internal oxidation.
The intermediate hose is one of the latest super-flexible braided variety. Like some other regulator manufacturers that employ these hoses, Mares claims that they are made to the companys own specification, but it looks just like an Italian-made Miflex hose.

Second Stage
The second stages case is constructed entirely from SMC carbon fibre, 65% lighter than a similarly made metal version. It is said to have better heat-conducting qualities than metal, so should be ideal for diving in cold fresh water.
Even the ventilated hose protector that covers the point at which the intermediate hose is connected is said to be a better heat conductor than those normally used.
A mesh grid is incorporated into the design. Should a diver face a strong oncoming current while perhaps hooked off to a bit of substrate, the water meeting the pressure-sensing diaphragm inside the second stage is nicely diffused, preventing unwanted purge effects.
SMC stands for Sheet Moulding Compound. This new technology, adapted from Formula One racing, allows the regulator designer to specify a complex shape that includes the Mares patented Bi-pass tube.
This tube sends air directly to the mouthpiece rather than across the back of the pressure-sensing diaphragm, where it could cause a localised drop in pressure and consequent exponential free-flow in some circumstances.
This removes the need for any knobs, switches or other manual adjustments.
I am not enamoured of the finish. It has the look of a prototype, and reminds me a little of plastic that has been shattered by heat or cold. I didnt test it to see how well it would withstand a diver standing on it in the RIB - the people with whom I was diving were too considerate.

Purge Control
The control is easy to feel for, because it is a distinct plastic button. This pushes onto the internal plastic grid and activates the lever that is otherwise controlled by the pressure-sensing diaphragm, to open the second-stage valve.
It was straightforward to use, and there were no surprises with either a weak flow or an uncontrollable gush of air.

Comfort
Mares claims that the Carbon second stage eliminates that dry-air effect sometimes encountered during lengthy warmwater dives.
I found that it felt unnaturally large, though it was never heavy. Thats because its dimensions will be more familiar to those divers used to the regulators designed, say, five years ago, rather than the much smaller designs currently available. The distance from the mouthpiece to the front of the diaphragm is about 13cm, which is quite a lot by todays standards.
The flexible braided hose meant that the route from the first stage gave little resistance, and I never felt that if I turned my head to the left the mouthpiece might be pulled from my mouth.
The Carbon 42 always gave me enough air when I needed it, but I was conscious of perhaps having to suck a little harder than I would expect with some other Mares regulators.
Thank goodness Mares has done away with the somewhat floppy mouthpieces it has employed in the past. This one is as good as any Ive used.

COMPARABLE REGULATORS TO CONSIDER:
Scubapro MK11T/S555, £679
Sherwood SR1, £379
Apeks Flight, £341

SPECS
PRICE £530
FIRST STAGE Diaphragm
PORTS 4 mp and 2 hp
SECOND-STAGE Carbon fibre
SECOND-STAGE ADJUSTMENTS None
SECOND-STAGE COLOURS Black (Octopus black and yellow)
DRY WEIGHT 1kg
CONTACT Head UK, 01539 724740
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