Product Reviews

The truth I’ve learned after wearing them for two years: if you're going to wear them in summer, which is actually better—RAL COOLMAX MERINO or 100% MERINO WOOL?

2026/7/30 石川大稀

I’ve recently been hooked on an activity called “Bike to Hike.” I’m Ishikawa.

I’ve been enjoying it while learning plenty from some experienced climbers.

I cycle to the foot of a mountain, get off the bike, and climb. Once I head back down, I get back on the bike, stop by a sento (public bath), grab a delicious meal, and head home.
This kind of day is simply the best—it’s my favorite holiday routine.

What I’ve realized again is that cycling and mountain climbing share so many similarities.
Both allow you to experience something outside the ordinary.
They both make you feel like you’re on a journey.
And, most importantly, the breaks are the absolute highlight.
(The food and the bath truly become the best moments of all.)

And one more thing:

“The clothes you wear are almost entirely interchangeable.”

My regular riding gear works just fine for low-altitude mountains.
As I looked into apparel for climbing, I found that one material appeared almost every time: “merino wool.”

When it comes to merino wool, the RAL COOLMAX MERINO TEE, which I’ve worn nearly 100% of the time during my rides for the past two years, is the first thing that comes to mind.

It’s my personal favorite.
The fabric is a blend of 50% merino wool and 50% polyester.

When I look at the gear worn by experienced climbers, I often see them wearing 100% merino wool.

Polyester blends versus 100% merino wool—which is actually better!? What’s the real difference!?
To compare, I bought a few 100% merino T-shirts and wore them for rides, hikes, and as everyday clothes to see how they stack up.

In this post, I’ll share how the "RAL COOLMAX MERINO Tee" and "100% MERINO WOOL" actually differ in ways you can’t see on a spec sheet.

I’ve compared them based on my own personal experience.

First, I’ve summarized the key points from my experience in a table.

To give you the conclusion first: If I’m wearing it in the summer, I’m choosing the RAL COOLMAX MERINO Tee.

Before we compare... wait, wool in the summer?

“Isn’t wool a winter material?”

That’s what I thought at first, too.
But in the worlds of mountain climbing and hiking, merino wool has long been a staple material.

It has natural humidity control, wicking moisture while absorbing sweat.
It has natural anti-odor properties, so it stays fresh even when you sweat.
It also offers natural UV protection, making it a beloved material that stays comfortable even in hot weather.

That’s why so many people choose "wool" even in the summer.

However, merino wool does have its weaknesses.

When you sweat a lot, the fabric can feel heavy as it retains moisture.
It takes a little longer to dry.
It’s a delicate material if you want to wear it every single day.
You need to be careful with washing and care (to avoid shrinking or losing shape).

To address these weaknesses, RAL uses a blend of 50% merino wool and 50% COOLMAX® polyester.

By combining the comfort and anti-odor properties of merino wool with the excellent moisture-wicking and quick-drying capabilities of COOLMAX®, it becomes a shirt that dries fast even when you sweat and is easy to maintain.

On paper, it looks like it has the "best of both worlds," but is there really a difference when you wear them?

From here on, I’ll share my findings from wearing these in various settings: riding, climbing, and casual daily use.

Comparison ① Mid-summer comfort and drying speed

100% MERINO WOOL offers a sense of security because it absorbs sweat very well.
However, when riding in the scorching summer sun or climbing, the heavy sweating made the fabric feel weighed down and it tended to cling and get sticky against my skin.

Since it also takes a while to dry, there were definitely moments in the middle of summer when it felt problematic. (You would definitely need an undershirt to soak up the sweat in high-heat situations.)

On the other hand, the RAL COOLMAX MERINO Tee has significant quick-drying ability thanks to the COOLMAX®. Even when drenched in sweat, the breeze during a break dries it off quickly—that’s the classic COOLMAX experience. It feels light and dry against the skin, making it much less uncomfortable.

For mid-summer rides, climbing, or any activity where you expect to break a major sweat, the RAL COOLMAX MERINO Tee takes the prize.

Comparison ② Skin feel

Here, 100% MERINO WOOL takes the prize.

The softness the moment you slide your arms through the sleeves is truly comfortable and addictive. I always find myself thinking, “Man, 100% MERINO WOOL really feels amazing.”

I’m a big fan of the MERINO MERINO, and the comfort is truly outstanding.

The RAL COOLMAX MERINO Tee is certainly comfortable enough, but it doesn't quite match that plush, gentle texture of 100% merino.

I feel that 100% MERINO WOOL is very well-suited for low-intensity activities. It’s perfect for camping, rides in cooler weather, light hiking, traveling, or just everyday wear; the comfort level is truly unique.

Comparison ③ Odor resistance

In this area, I really felt the distinct advantage of merino wool in both shirts.

Even after sweating on a ride and getting home, the shirts don’t hold much odor—I’ve often felt, “I could probably wear this again today.” Even if you’ve sweated buckets on a mountain, popping into a café afterward isn’t a problem.

Of course, they aren't completely odorless. But compared to 100% polyester or cotton T-shirts, the difference in how much sweat odor persists is clear.

Based on wearing both, the difference is very slight, but I felt that 100% MERINO WOOL had a slight lead in anti-odor performance.

For travel, bikepacking, long touring, or climbing—scenarios where you might wear the same clothing for days at a time—this high level of odor resistance is more reliable than you might imagine.

That said, the RAL COOLMAX MERINO Tee never gave me any cause for concern regarding odor on day trips or in daily life; it performs more than well enough for practical use.

Comparison ④ Washing and durability

This is an important point if you plan to wear them frequently.

I made a mistake when washing my 100% MERINO WOOL shirt.
I used mild detergent on a gentle cycle (hand-wash/delicate setting) and flat-dried it to keep its shape, but it still shrank more than I expected…

I understood it was a delicate material and maybe my washing technique wasn’t perfect, but it shrank in length so much it became practically unwearable… It was a good lesson for me regarding size selection (sob).

On the other hand, I’ve been wearing the RAL COOLMAX MERINO Tee nearly every week for the past two years. (I wore it as a base layer in fall/winter and on its own in spring/summer.)
I use a laundry net, but I don’t use any special detergent and just toss it in the washing machine. (Sorry for being a bit rough with it.)

※ I do avoid using the dryer, though.

Even so:

• No fraying at the collar or sleeves
• Almost no shrinking
• It holds its shape well
• Resists wrinkles
• No pilling

Those were the results.

The collar and sleeves use the same COOLMAX MERINO fabric as the rest of the shirt, so they don’t get stretched out or saggy.

Maybe a material that handles this kind of rough treatment is better for someone as lazy as me.

So, which one should you wear in the summer!?

As the title of this blog suggests, if I have to choose "the one shirt to wear in the summer," I can confidently recommend the RAL COOLMAX MERINO Tee.

However, the bottom line is that it isn't about which one is "better," but rather that each has its own preferred scenes and seasons.

Recommended scenes/seasons for the RAL COOLMAX MERINO Tee:

When you want to wear it for high-sweat activities
When comfort is your top priority in the middle of summer
When you want to wear and wash it without worrying about wrinkles or maintenance

Recommended scenes/seasons for 100% MERINO WOOL:

When spending relaxed time like camping or traveling
When enjoying lighter, low-intensity activities
When you want a piece that works well into the fall and winter
When the feel and comfort against the skin are your top priorities

My thoughts after two years of wear

Two years ago, I started wearing it with a bit of skepticism: "Wool in the summer?"

But now, it’s the first thing I reach for when summer arrives.

It’s comfortable even when you sweat.
It dries quickly.
It doesn’t retain odors.
It handles washing well.

And on top of that, I can wear it for cycling, climbing, traveling, and just living my daily life. That’s why, before I knew it, I’d been wearing it consistently for two years.

For days like mid-summer rides or Bike to Hike adventures, where I’ll be sweating and playing all day, I choose the RAL COOLMAX MERINO Tee without hesitation.

Of course, if skin feel and odor resistance are your absolute top priorities, then 100% MERINO WOOL is a valid option. But for me, as I am today—wanting to enjoy every bit of summer comfortably in just one shirt—this T-shirt is the perfect match.

If you’re thinking “Wool in the summer?” just like I was two years ago, I highly recommend giving it a try.

I’m certain it will change your perspective entirely.

RAL Merino Coolmax S/S Tee