As a mountain biker, you know how crucial clear vision is for both your safety and enjoyment on the trails. Foggy goggles or glasses that limit your visibility are extremely annoying but a very common problem that’s hard to get rid of. Perhaps you’ve even tried numerous models to prevent fogging, but nothing seems to work as well as you’d hoped. Fogging can occur even with high-quality equipment, and sometimes it feels like an endless battle to keep your vision clear.

Key takeaways:

Good ventilation is the single most effective way to prevent goggles and glasses from fogging up. Airflow can be improved by proper fit, removal when there’s no airflow, and goggle design. No amount of anti-fog coating is going to help when humidity or moisture is trapped inside.

When mountain biking, airflow isn’t always available. That’s why fogging goggles are such a big issue in MTB compared to motocross, even though the goggles are the same. There are ways to eliminate fog tho, even when going uphill.

fox vue mtb goggle top vent
Can you spot the difference? The bottom goggle is well-ventilated, and the top one restricts airflow.

But that’s just the quick summary. In this guide, we will address the reasons behind fogging in MTB goggles and glasses and provide you with practical tips and solutions that can make a real difference. And they are completely free and help immediately!

Preventing fogging goggles depends more on the rider wearing them, than the goggle itself.

Let me explain that by looking at the reasons why goggle lenses get blurry in the first place. Hint: It’s rarely actual fogging.

Why MTB Goggles Fog Up

Basically, there are two main conditions that lead to milky or blurry vision wearing goggles or glasses:

  1. Fogging (milky glass vision) due to temperature differences between the two sides of the lens leads to condensation.
  2. Humidity between the face and the inside of the lens of the goggles or glasses lens resulting in a wet lens.

As you can see, the criteria for fogging through condensation only occur in specific conditions. While body temperature is fairly constant, ambient temperature is the biggest factor here. This is why actual fogging (like looking through milky glass) only happens in colder temperatures, not on hot summer days when the outside temperature matches your body’s.

The most common issue is humidity and moisture trapped on the inside between the face and lens. Water droplets accumulate making vision blurry. Beads of sweat can even directly drop onto the lenses.

melon mtb goggle vent
Bottom foam liners may be removed for better airflow while still not getting debris inside. Top ones should be left, especially in wet weather.

In other words, mountain bike goggles and glasses can “fog up” due to various reasons, related to differences in temperature, and excess humidity, and moisture. Here are some specific reasons for fogging:

  1. Temperature difference: When there is a significant difference between the temperature inside the goggles/glasses and the temperature outside, fogging can occur. This is because the warm air inside the goggles comes in contact with the cooler lens surface, causing condensation.
  2. Humidity: High humidity levels can also cause fogging, as moisture in the air tends to condense on the cooler surface of the lenses.
  3. Sweat and moisture: Most of the time, the humidity will come from your body as it generates heat and sweat. If the goggles or glasses are not well-ventilated, this moisture can accumulate on the inside of the lenses and cause fogging.
  4. Lack of ventilation: All of the above issues are increased by a lack of airflow. Adequate ventilation is essential to prevent fogging. If the goggles or glasses do not have proper venting, it becomes difficult for the moisture and heat to escape, leading to faster and increased fogging.
  5. Poor fit: Especially glasses that don’t fit well can trap warm, moist air near your face, contributing to fogging.
  6. Lack of anti-fog coating: While coating does help, it only contributes little compared to eliminating the above issues. It will not bend the physics so it’s important to know how and why fogging occurs in the first place.

Tips for Preventing Fogging

Now that we know what exactly leads to blurred vision, we can think about specific ways of stopping fogging goggles by eliminating the individual underlying issue specific to you.

Selecting models with adequate vents

Proper ventilation is the most important solution for preventing goggles from fogging up. It starts with picking goggles with vents that allow air to flow through, reducing the amount of moisture that builds up inside. Those are found on the top, sides and bottom and are covered in a foam liner. The number and size of those vents vary, and so does the foam thickness.

melon mtb goggle bottom vent
fox vue mtb goggle bottom vent

If in doubt, you can still easily modify the goggles you got by cutting holes into the foam covering the top and bottom. Or removing it entirely. But for starting out, leave the top as it is because it’s crucial to keep dirt and grime out, especially in bad weather.

Air circulation during breaks

This is the biggest mistake riders make most often. It’s an extra step for managing the goggles that’s often forgotten. But it’s the best and easiest way to stop moist lenses.

During breaks, the body is heated up from exhaustion but any airflow is stopped. The perfect way to trap some moisture! Just remove the goggles or glasses and put them on your helmet. Or lift the goggles up periodically for short breaks. Or move the glasses further down your nose for some much-needed airflow. Pick at least one and only put it on when you’re about to move again.

Periodically allow fresh air to circulate inside the goggles or glasses when stopped

Once moisture accumulates on the lense’s surface, it’s hard to get off without smearing it all around. Don’t let it get this far in the first place.

A Giro Switchblade MTB Helmet from the side with the visor tilted up
Some helmets allow goggles to easily slide up to get the out and away from the heat source: your face.

Ensure a Good Fit

A good fit is essential for preventing glasses from fogging up. Generally, the further away from the eyes, the more air can circulate and the more air volume is there as a buffer. That’s why MTB glasses are usually rather big. Look for ones that don’t quite seal to allow for constant airflow. They should fit well and comfortably without touching your face all around the frame.

Goggles should generally fit snugly against your face and create a seal around your eyes. So fit isn’t really adjustable. But certain more expensive models help by having the goggle straps elevated from the goggle frame. It’s more of a benefit for comfort rather than help with fogging tho.

melon mtb goggle side vent
Goggles and glasses have varying widths and heights to match your face and head shape.

Keep Your Face Dry

Another problem is beads of sweat actually making contact with the lenses by dripping on them. This can easily happen with the usual body position on a bike, with the head tilted down.

Consider using a moisture-wicking helmet liner to help absorb sweat to stop it from pouring down your face. Use a towel to wipe away any sweat or moisture from your face before putting on your goggles. This will reduce the amount of moisture that enters the goggles and condenses on the lens.

Choose goggles or glasses with anti-fog coatings

I am personally not a fan of lens coatings and additional products like anti-fog sprays, to be honest. No amount of coating is going to save your goggles from fogging when you’re sweating and there’s no airflow. Coating doesn’t bend the underlying physics. It only helps the last few percent when you’re doing the above steps.

I have to cover it for sake of completeness but in my experience, anti-fog coating doesn’t make a huge difference. I wouldn’t advise spending extra on those kinds of lenses if you have the choice. Better ventilation is going to be more helpful.

So make sure to cover your bases on the most important things you can do before spending on the little improvements.

Get fitter

What is this dude on about now? Let me explain.

We established that humidity and moisture coming from the body is the main culprit for limited vision. Why not attack the problem right at the source? While some people do generate more sweat than others, fitter riders generally don’t get as hot as unfit ones. Just because the same amount of output requires less exhaustion. A bigger engine simply doesn’t run as hot.

Now, this isn’t an overnight solution, but more of a long-term improvement. But if you’re interested in this alternate way, and maybe don’t know how and what to do for training, I got just the resource for you where I put my favorite MTB training exercises from beginner to advanced.


Fogging goggles can be a frustrating problem, but it doesn’t have to ruin your MTB rides. By choosing the right goggles, ensuring a good fit, using proper ventilation, keeping your face dry, and maybe on top of that using anti-fog products, you can prevent fogging and enjoy crystal clear vision in any weather condition. It takes a little extra effort managing but it’s well worth it. Certainly better than not using any eye protection.