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  • Giro Fathom Helmet
  • Giro Fathom Helmet
  • Giro Fathom Helmet Side
  • Giro Fathom Helmet Side
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GiroFathom Helmet
Sale 35% Off$97.47 - $104.96

Item # GIR007J

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Item # GIR007J

The Atmos II's dirty brother.

After years of watching a wide range of athletes buy its beloved Atmos road helmet for off-road racing, Giro decided to go ahead and design a mountain-ready version of the new Atmos II, and so created the Giro Fathom Helmet. A structural clone of the Atmos II, boasting the new Thermoformed SL Roll Cage, the Fathom gets its own styling and a removable visor, making it just that much more ready to hit the trail.

The SL Roll Cage is the skeleton that gives form to the helmet's EPS liner. It keeps the helmet together under impact, acting like a second shell to maintain the helmet's structural integrity and disperse impact. The added strength also means that Giro can add negative space to the Atmos II without sacrificing safety, so it's more ventilated and lighter than its predecessor. The Atmos II still takes advantage of Giro's In-Mold Composite reinforcement, which permanently fuses the outer shell and SL Roll Cage to the EPS foam liner to enhance the effectiveness of all three.

In an age of mass production, Giro's Roc Loc 5 Fit System makes the Atmos II fit like a custom one-off. You can custom tune the fit tension as well as the fore-aft tilt of the helmet in seconds with one hand. Though other helmet manufacturers have similar adjustability options, none of them even come close to the weight savings that the Roc Loc system offers; it's almost 40% lighter than comparable systems.

Keeping your head cool during even the hottest, most critical road races is something that Giro has focused a great deal of attention on. Giro helmets are developed with a proprietary Wind Tunnel Ventilation System that combines 26 vents in the shell with exhaust channels within the belly of the helmet leading to the rear. Fresh, cool air from the front is strategically channeled around the head to help evaporate the sweat before exiting through the rear exhaust openings. It's a natural cooling system that you'll appreciate every ride.

  • Roc Loc 5 adjustment system
  • SL Roll Cage maintains helmet’s integrity in the event of a crash
  • Removable Visor
  • 26 Wind Tunnel vents move air in, through, and out of the helmet
Tech SpecsSize
Tech Specs
Shell Material
in-mold polycarbonate, Thermoformed SL Roll Cage
Impact Foam
23 Wind Tunnel vents, internal channeling
Fit Adjustment
Roc Loc 5
yes, removable
Recommended Use
cross country
Manufacturer Warranty
1 year


Adult Cycling Helmets
Super Fit™
Head Circumference

18.5 - 20in

(47 - 51cm)

20 - 21.75in

(51 - 55cm)

21.75 - 23.25in

(55 - 59cm)

23.25 - 24.75in

(59 - 63cm)

24 - 25.55in

(61 - 65cm)

Head Circumference

21.25 - 24in

(54 - 61cm)

19.75 - 22.5in

(50 - 57cm)

22.75 - 25.5in

(58 - 65cm)

How to Measure:
For best results, use a tape measure to measure around your head where your hat would fit comfortably.

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super light

    I've been looking for a new mnt biking helmet for awhile. I have a hard time finding one that fits because I'm in between S and M sizes (56ish cm). Small sizes usually are too tight in temples, while mediums do not tighten enough to feel secure. I ordered this helmet in size Small and it fits well, I have room to add one thin layer if it's cold and it can be tighten securely around my head even with a pony tail. It's very light, which is great for me since most of my riding is xc. (I wonder is it compromises safety though?) With a few simple adjustments it stays comfortably secure without bulky weight or extra bells and whistle. It's a little costly, which is the main downside of this helmet.

    Perfect for all situations

    • Familiarity: I've used it several times

    I'm a newbie when it comes to biking, but I can say that this helmet seems good for all situations, from a chill ride to a more demanding activity.
    I really like how light and the level of ventilation this helmet provide!
    It's really confortable, awesome fit and it also look good.

    Great airflow and light

    • Familiarity: I've put it through the wringer

    Fit is excellent no dropping down in eyes on even the roughest terrain. Best suited for XC racing.

    Light and Tight

    • Familiarity: I've put it through the wringer

    I've been wearing Giro helmets for years and am thrilled to have upgraded to this one. The size adjuster is smoother and has more settings than prior helmets. Tons of venting and it is so light that you barely notice it's there. I just hope it offers the same protection if i bump my cabeza!

    Long time Giro user looking elsewhere

    • Familiarity: I returned this product before using it

    I've been a HUGE proponent of giro helmets and have been wearing them exclusively for the last 10+'years. The mediums fit my head like a glove and I am currently running a synth on the road (love it) and Giro Montaro for mountain.

    I ordered the fathom for a lighter XC helmet and out of the box this does NOT fit like other giro helmets as it is extremely shallow and provides very little coverage. Additionally, I was never able to get the straps to lie flat against my face, the buckle is extremely off center and and the fit is generally off. The visor is crooked (and tiny) and the helmet had a super cobby unfinished look with excess foam etc. This is the WORST effort I have ever seen from Giro. Very disappointed.

    Meets the hype!

    • Familiarity: I've used it several times

    The Perfect helmet as described by everyone

    Fantastic helmet!

      I love this helmet. It is so light, I barely feel it on my head. I love the look and color of it. The adjustment system is super easy to do one handed while riding.

      Just starting to test

      • Familiarity: I've used it several times

      Because of a very wet spring here in Utah I have not had the chance to use this much. The fit seems good so far. I will update this as I get more rides in.

      Now if have several rides in the mid summer months with this helmet and it is working great. Light and airy. I am stoked.

      Light & Cool

      • Familiarity: I've used it several times
      • Fit: True to size

      Live in hot and humid Houston. I replaced an older Giro road helmet with a real visor that blocked the morning sun, that helmet also routed the sweat in the front around your face and no sweat drip on glasses and face until the pads wore out.

      The new helmet is smaller looking lighter and well ventilated, fits well and adjustable. It is cooler than the old one.

      Only negatives are the visor is useless for blocking morning sun.
      I removed it and went back to using a chopped cycling cap for morning sun and there are vents in front that do help cool better but you do get sweat drip.

      Perfect mtn bike helmet

        Great fit, the straps are smaller which feels better. Awesome venting. This should last me a long time. Good value.

        Great XC Helmet

        • Familiarity: I've put it through the wringer

        Love this helmet for XC riding. It is so light, comfy, and airy that it feels like I'm not wearing anything.

        The Roc Loc 5 is awesome and easily adapts to headshape, hairstyle, and head coverings. You could for sure wear a bandana or skullcap under this helmet and still be comfortable. But then again I don't know why you would, it's just so well ventilated! I've definitely taken a few hard spills and it's showing no signs of damage.

        If you're looking for a go-to lightweight XC style helmet, this is it! You won't be disappointed.

        I'm a Large in most head apparel (I guess I'm filled with hot air) and this helmet was no different.


        Great XC Helmet

        Awesome and well vented XC helmet

        • Familiarity: I've used it once or twice and have initial impressions

        Rode with the helmet during an Israeli spring heatwave (+30 c). Awesome ventilation, immediately you feel the air flowing all over your head. Trumps previous specialized S-works helmets with good ventilation themselves. The giro isnt as lite as the S-works but also not as expensive. If your helmet needs to be safe and vented, this is definitely the helmet for you!
        Giro could learn from specialized when it comes to strap endings and length that are very long and dont really solve dangly straps. I personally dont find this a big deal as the rest of the design is very aesthetic.

        Great warm weather MTB Helmet

        • Familiarity: I've used it several times

        Living in FL, I prefer a helmet that has a lot of venting, is lightweight, and is comfortable. The Fathom does all three while still providing better protection than using a straight-up uber-light road helmet. The new wider straps and roc-loc retention make this thing very comfortable too.

        A couple other little features I like are the removable visor and the small rubber plugs you put in the visor holes on the helmet to give it more of a finished look with the visor off. Also dig the extra set of pads.