The brief
What is actually protecting your eyes
Light category, filtration and fit are the three variables that decide whether a pair of sunglasses helps or hurts you on a long day out. Here is how each one works, and how to pick.
Start here
Bad sunglasses are worse than none
A dark lens makes your pupil open. If that lens does not filter UV, you have just widened the door for the exact radiation you were trying to avoid. This is not a scare story — it is why cheap unlabelled sunglasses are a genuine eye-health risk rather than a harmless compromise.
It is also why every MUCHi lens carries the UV400 mark and blocks 100% of UVA and UVB across the entire lens surface, including the edges. Not 99%. Not "UV protection". Full, measured filtration, on every model including the $69 one.
Reference table
Light category, and where each one belongs
Light category describes how much visible light reaches your eye. It is regulated under EN ISO 12312-1 in Europe and mirrored by equivalent standards elsewhere. Picking the wrong one is the most common mistake in outdoor eyewear.
| Category | Light transmitted | Where it belongs | What to know |
|---|---|---|---|
| Cat. 1 | 43–80% | Deep shade, dawn and dusk, overcast forest | Very light tint. Not enough for exposed terrain at midday. Photon Shift starts here before it darkens. |
| Cat. 2 | 18–43% | Changeable conditions, mixed woodland | A genuinely useful middle ground in spring and autumn. Rare in dedicated outdoor eyewear. |
| Cat. 3 | 8–18% | Almost all daytime hiking, running, riding and general outdoor use | This is the default. If you are buying one pair and your route does not cross snow, buy this. Legal for driving. |
| Cat. 4 | 3–8% | High-altitude snow, glacier travel, mountaineering | Necessary on snow, where you receive direct sun plus near-total reflection. Not legal for driving in the EU and dangerous on roads. |
Four decisions
Where the build quality actually lives
Materials
Four materials, chosen for one property each
Memory polymer
A nylon-based thermoplastic that flexes and returns rather than snapping. Ours is what lets us remove the hinge plate entirely on running models — less material, fewer failure points, and a frame you can twist in a pack without breaking.
Cold-weather chassis
Standard thermoplastics get brittle below freezing, which is exactly when you are wearing mountaineering eyewear. Grilamid stays flexible to roughly −20 °C, so Summit X does not crack when you drop it on a boulder at altitude.
Hand-finished sheeting
Drift uses a plant-based acetate sheet that is cut, tumbled and polished over three days. Colour runs through the material rather than sitting on the surface, so it does not wear through at the temple tips — the usual failure in acetate eyewear.
Grip that improves wet
Most rubber gets slippery with sweat. Hydrophilic compounds absorb surface moisture and swell slightly, which increases friction against skin. Fitted to every nose pad and temple grip across the range — the single cheapest upgrade to any sport frame.
Field care
Most coating damage is self-inflicted
Trail dust is abrasive. Wiping a dusty lens dry grinds that grit into the coating, and once the hydrophobic layer is scuffed the lens fogs more and cleans worse. Every scratched lens we see came from this, not from sunlight.
- Rinse under running water first. Always.
- Wipe with the supplied microfibre pouch, never a shirt or a towel.
- Keep sunscreen and insect repellent off the lens — alcohol and DEET attack coatings permanently.
- Store in the case, not loose in a pack with a metal water bottle.
- Never leave them on a car dashboard. Heat warps acetate and delaminates coatings.
Pick by the terrain you actually ride
If it is trails, take Cat. 3 with polarisation. If it is snow, take Cat. 4 and a sealed shield. If it is both across a season, own two — it is cheaper than one compromised pair.