SaySky Flow 2.5L Waterproof Jacket Review: Featherweight Rain Protection for Runners

Introduction

A good quality running waterproof jacket has become an essential piece of kit, especially if you live somewhere that gets its fair share of rainy days. The Flow 2.5L Waterproof Jacket from Danish apparel brand SaySky is a new, deliberately stripped-back option built around one idea: make a genuinely waterproof jacket so light and packable that you never leave it behind.

On paper, the numbers are striking. It carries a 20,000mm waterproof hydrostatic rating, a 20,000g/m²/24h breathability rating, packs down remarkably small, and weighs just 110g in a medium, which is exceptionally light for a 2.5-layer waterproof. That performance comes at a price though: it retails for £259 on the SaySky website in the UK. After more than a month of testing in wind, rain, and cold, here is how it holds up.

Who This Jacket Is For

SaySky designed the Flow as the perfect packable companion on rainy days, whether you are hitting the roads or heading out on the trails. The construction reflects that: an extremely lightweight fabric with a waterproof breathable membrane, an ultra-thin nonporous moisture-permeable PU film, and a ripstop shell with taped seams. It comes in five unisex sizes from XS to XL, in a single all-black color option.

If you count yourself among the runners who want kit to be ultra-lightweight and stripped back so it never holds you back, this is exactly where the Flow comes into its own. It is a jacket built for moving fast through bad weather, not for standing still in it.

Main Strengths

The first thing you notice is how ridiculously light it is. Hold the jacket up to a light and you can almost see through the fabric, which underlines how thin it is, yet it still offers a genuinely good level of protection from the elements. Among lightweight waterproof running jackets tested over the years, this is the lightest yet at 110g in a medium.

The hood is a well thought-through feature. Elastic running down the sides pulls it in snug around your face, a small toggle at the back allows personal adjustment, and a clever internal mesh membrane holds the hood securely while helping with breathability. Turn your head and the hood moves with you, leaving you feeling cocooned in the jacket, which is a real comfort in harsh conditions. The internal mesh panel is a feature SaySky also uses on its Element 3L jacket, and it works just as well here.

In wet training runs the jacket performed well. The DWR coating beaded water quickly, and with the hood pulled in tight it felt like it was providing great protection. Taped seams, a quality YKK zip, elasticated hem and sleeve cuffs, an internal hanging loop, and reflective transfers on the arms and back round out a clean, minimal feature set.

Packability is the other standout. The Flow scrunches down to roughly the size of a tennis ball, which is ideal if you run with a belt or vest. On more than one occasion a run started in rain, the weather cleared mid-way, and the jacket simply came off, scrunched up, and disappeared into a running belt. There is also a race-day benefit: with a 20,000mm hydrostatic rating it will pass most mandatory kit checks while taking up very little room in a race vest, leaving space for everything else you need to carry.

Things to Consider Before Buying

For all its appeal, the Flow makes a few compromises worth knowing about. There is not a pocket in sight. That is partly personal preference, since some runners dislike items bouncing around in jacket pockets, but it is a real limitation if you like stashing gels or gloves.

A missing ventilation feature is more of a genuine gap. Many running waterproofs now include a press stud partway up the zip, so you can unzip for airflow while keeping the jacket from flapping around. The Flow is all about saving weight, but a small press stud would barely have affected the 110g figure and would have worked really well here.

Sizing also deserves attention. The recommendation from SaySky was to size up to a large, but in practice that felt a touch big, and a medium, the usual size in other SaySky apparel, would likely have fit better. The Flow appears to run true to size. That matters, because an oversized waterproof leaves excess material that creases and channels water, which can wet out the fabric and stop it doing its job.

Buying Advice

The key question is what you want a waterproof to do. For racing or fast training, where minimal weight and packability matter most, the Flow is an excellent choice: it disappears into a vest or belt and provides solid protection while you keep moving.

For long days out where you might be caught in bad weather for hours, a more robust option may serve you better. SaySky’s own Element 3L jacket is the obvious alternative. As a three-layer design it is not as light or as packable as the Flow, but it is still reasonably compact and offers long-lasting protection no matter how harsh the elements, which is what matters when you are high in the mountains or on a long coastal stretch and the weather turns.

If your priority is guaranteed shelter through hours of storms, lean toward the 3L. If your priority is always having a capable waterproof with you without noticing it is there, the Flow is hard to beat.

Conclusion

The SaySky Flow 2.5L Waterproof Jacket is the lightest waterproof of its kind that we have tested, weighing 110g in a medium while still delivering a 20,000mm hydrostatic rating, strong breathability, a secure and comfortable hood, and tennis-ball packability. Its stripped-back design means no pockets, no zip ventilation stud, and a level of protection best suited to faster, shorter stints in bad weather rather than all-day exposure. At £259 it is a premium purchase, but for runners who want ultra-light kit that never gets left behind, it delivers exactly what it promises.