The 37.5 fabric is a game-changer for more than just athletes

Gerda Engelbrecht

Whether you’re pushing through a HIIT session, tackling weekend trails, or managing the unpredictable temperature swings of menopause, First Ascent’s new 37.5 range offers science-backed comfort that adapts to your body. This isn’t just another moisture-wicking fabric – it’s intelligent thermoregulation that works.

There’s a particular type of discomfort that comes with synthetic activewear: that clammy, sweat-soaked sensation when you’re working hard, followed by the creeping chill when you stop moving. For years, we’ve accepted this as the trade-off for performance clothing. But First Ascent’s new range featuring 37.5 Technology challenges that compromise entirely.

I’ve spent the past month testing two key pieces from the collection – the Performance Baselayer Long Sleeve and the Alto Jacket – and the results have been revelatory enough to change how I think about technical clothing.

What makes 37.5 Technology different?

Before diving into the individual products, it’s worth understanding what sets 37.5 apart from conventional moisture-wicking fabrics. The name itself refers to your body’s ideal equilibrium: a core temperature of 37,5°C and relative humidity of 37,5% in the microclimate next to your skin.

The technology works through billions of active particles – derived from volcanic minerals and coconut-shell activated carbon – permanently embedded at the fibre level. These particles create an ultra-porous structure that massively increases the fabric’s surface area, allowing it to capture moisture at the vapour stage before it condenses into liquid sweat.

Here’s where it gets clever: the particles absorb infrared energy naturally emitted by your body, using that energy to accelerate evaporation when you’re hot. When you’re cold, that same infrared absorption helps retain warmth. It’s dynamic thermoregulation powered by your own body heat.

Unlike coating-based treatments that wash out over time, these particles are woven into the fabric itself, meaning the performance is permanent. The particles also trap odour molecules and release them during washing – a feature that becomes particularly appreciated after intense training sessions.

Why this matters beyond the gym

While athletes will immediately recognise the performance benefits, the real game-changer is how broadly useful this technology is. Women navigating perimenopause or menopause deal with sudden, unpredictable hot flushes caused by fluctuating estrogen and progesterone levels, which directly affect the body’s thermoregulation mechanisms. Clothing that actively manages temperature and humidity – removing moisture vapour before you even feel overheated – can significantly improve comfort during the day and night.

Similarly, anyone who experiences temperature sensitivity, works in variable environments, or simply wants to feel comfortable throughout the day will find genuine value here. This is technical clothing that’s sophisticated enough to wear beyond the trail.

The Performance Baselayer Long Sleeve: Tested to the Limit

• Price: R699
• Composition: 73% 37.5 Polyester, 15% Polyester, 12% Spandex
• Fit: Slim

I tested this baselayer in arguably the most punishing scenario possible: indoor cycling sessions on a Zwift bike where sweat is inevitable and ventilation is limited. Over four weeks of regular use, the fabric’s performance remained consistent and impressive.

The slim fit provides compression without restriction, and the 12% spandex content means the garment moves with you rather than against you. But the standout feature is how it manages moisture. Where traditional baselayers would become saturated and heavy within 20 minutes, the 37.5 fabric stayed remarkably dry to the touch. You sweat, certainly, but the vapour is pulled away so efficiently that you never feel sodden.

The fabric also dries extraordinarily quickly between intervals or when cooling down – a detail that prevents that post-workout chill. After a month of testing and regular washing, the performance hasn’t degraded, and crucially, there’s no lingering odour even after particularly intense sessions.

For runners, hikers, or anyone engaging in sustained aerobic activity, this baselayer excels at maintaining comfort across varying intensity levels. It’s equally effective as a standalone layer during warmer conditions or as part of a layering system in winter.

The Alto Jacket: Where technical meets respectable

• Price: R1 299
• Composition: 55% 37.5 Polyester, 45% Recycled Polyester
• Features: Thermo-adaptive fleece, waffle texture

The Alto Jacket deserves particular attention because it succeeds in an area where most technical outerwear fails: it looks good enough to wear when you’re not exercising.

I discovered this during a morning run when an elderly couple pulled up alongside me in their bakkie, visibly concerned. They thought I was in trouble – that someone was chasing me or that I was frightened – and stopped to offer me a lift to safety. I wasn’t even offended! It’s a testament to how the jacket reads: not as high-visibility athletic gear that screams “I’m exercising”, but as everyday outdoor clothing. The couple genuinely couldn’t tell I was out for a deliberate run.

The jacket’s clean lines and textured finish give it a more refined appearance than typical sports fleece. I’ve since worn it to the office on chilly mornings without feeling inappropriately dressed, which speaks to its versatility.

But don’t mistake style for a lack of substance. The thermo-adaptive fleece construction delivers genuine warmth without bulk, making it ideal for those in-between temperatures where you’re not quite cold enough for a puffer but need more than a shell. The waffle texture adds visual interest while creating air pockets that enhance insulation.

During hiking and trail running tests, the jacket performed brilliantly across varying exertion levels. On ascents, where you’re generating significant body heat, the 37.5 technology prevents overheating by actively managing humidity. On descents or exposed ridges, it retains enough warmth to stay comfortable without needing to add layers.

The weight-to-warmth ratio is particularly impressive. It’s light enough to pack into a running vest or day pack, yet provides sufficient insulation for early morning starts or unexpected weather changes. For South African conditions – where you might start a hike in single-digit temperatures and finish in midday sun – this adaptability is genuinely valuable.

The Performance Baselayer Vest: Summer-ready versatility

• Price: R499
• Composition: 73% 37.5 Polyester, 15% Polyester, 12% Spandex
• Fit: Slim

While I haven’t personally tested the sleeveless vest yet, it’s the logical next addition to any 37.5 wardrobe. With the same fabric composition and technology as the long-sleeve version, it offers the same moisture management and thermoregulation in a format suited to warmer conditions or higher-intensity training.

The vest works particularly well as a baselayer under a cycling jersey, as a standalone layer for gym sessions, or for summer trail runs where full sleeves would be excessive. I’m also planning to sleep in it during summer months – the active temperature regulation and moisture management should be particularly effective for managing night sweats, keeping the microclimate comfortable without the clamminess that typically accompanies warm nights.

At R499, it represents the most accessible entry point into the 37.5 range and would be an excellent choice for anyone wanting to test the technology before investing in the full system.

The layering advantage

One detail worth emphasising: 37.5 Technology becomes more effective when you use multiple pieces in the system. The more active particles present across your baselayer, midlayer, and outer layer, the more efficiently the system can manage humidity. I’ve found the combination of the Performance Baselayer and Alto Jacket particularly effective for winter morning runs – the baselayer handles moisture next to skin, while the jacket provides warmth and wind protection without trapping humidity.

Who should consider this range?

The obvious audience is outdoor enthusiasts and athletes who demand performance from their gear. But the real beauty of 37.5 Technology is its relevance beyond traditional activewear demographics:

• Women experiencing perimenopause or menopause: The active temperature regulation can meaningfully improve comfort during hot flushes and temperature fluctuations.
• Commuters and office workers: The Alto Jacket bridges the gap between technical and casual wear, making it suitable for variable indoor-outdoor environments.
• Anyone with temperature sensitivity: Whether due to hormonal changes, medical conditions, or simply running hot or cold, clothing that actively adapts to your body provides tangible comfort.
• Minimalist travellers: Garments that work across multiple scenarios and weather conditions reduce packing needs.

Worth the Investment

At R699 for the baselayer and R1 299 for the jacket, First Ascent’s 37.5 range sits in the mid-to-premium category. But the pricing reflects genuine technological innovation rather than marketing hyperbole. These aren’t garments you’ll replace seasonally – the permanent nature of the 37.5 particles means performance doesn’t degrade, making them a worthwhile long-term investment.

I now own two of the Performance Baselayer Long Sleeves and the Alto Jacket, which tells you everything about my confidence in the range. I’ll definitely be adding the sleeveless vest before summer arrives – it’s the perfect complement for high-intensity training in warmer conditions.

For anyone frustrated with conventional activewear’s limitations, or simply seeking clothing that works with your body rather than against it, First Ascent’s 37.5 range delivers on its promises. Highly recommended.

First Ascent’s 37.5 range is available online at www.firstascent.co.za

This article was not sponsored. All opinions are those of the editorial team.