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X-Bionic Energy Accumulator V2.1



Best-in-class performance from a top-dollar baselayer

At every product is thoroughly tested for as long as it takes to get a proper insight into how well it works. Our reviewers are experienced cyclists that we trust to be objective. While we strive to ensure that opinions expressed are backed up by facts, reviews are by their nature an informed opinion, not a definitive verdict. We don't intentionally try to break anything (except locks) but we do try to look for weak points in any design. The overall score is not just an average of the other scores: it reflects both a product's function and value – with value determined by how a product compares with items of similar spec, quality, and price.

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The X-Bionic Energy Accumulator V2.1 is a fantastic baselayer. And given the price, that's exactly what you should expect. You won't be disappointed, though, this one really delivers. It's the best winter baselayer I've tried.

There's a veritable book of information on the swing tag of this baselayer, but let's pick out some of the tech. Essentially this is a fully woven synthetic first layer, but X-Bionic uses a big range of different weaves and constructions to regulate temperature and moisture.

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One of the main technologies that X-Bionic uses is something it calls 3D-BionicSphere. It's a three-dimensional weave that sits next to the skin, creating air pockets for insulation along with sweat traps that help to move moisture away from the body. The idea is that if you're working hard then the fabric deals with the sweat, preventing the baselayer from getting soaked, and when you're resting the air channels fill up with warm air to keep you well insulated.

X-Bionic Energy Accumulator V2.1 Turtle Neck - chest logo.jpg

On the shoulders and the elbows, X-Bionic uses a concertina-style expansion weave to make sure that when the fabric is stretched over those bits of your anatomy there's still plenty of insulation available. The Energy Accumulator V2.1 also features air conditioning channels which are created using a raised weave either side of a flat weave. This creates a gap between the baselayer and the outer layer, allowing air to circulate.

X-Bionic Energy Accumulator V2.1 Turtle Neck - elbow.jpg

Does this all work? Yes. I've used this baselayer for all sorts of activity, and not just on the bike. Under heavy outer layers the Energy Accumulator V2.1 never gets swamped, and at the end of hard rides it's still been dry to the touch. The times you're most likely to feel the chill in my experience are when you've been working hard, on a climb, say, and then you have to stop and wait to regroup. That's when you find that your baselayer struggles to cope with a build-up of sweat when there's no air flow to help with surface evaporation, and the excess moisture can cool you quite quickly. That doesn't happen with the Energy Accumulator V2.1 top, it really does manage the moisture very effectively.

I've also had the opportunity to wear this baselayer while skiing in some fairly low temperatures (around -10°C) and it creates a very stable insulated environment when you're out in the cold but not physically working hard (that pretty much sums up my skiing). X-Bionic is heavily into skiing too, and it has a whole range of ski-specific kit; this baselayer crosses over between the two sports and it did a bang-up job. So if you're looking for something to use for longer, low-intensity riding in cold weather, or just general keeping warm, it should be high on the list for that as well.

> Check out our guide to the best baselayers here

The compression fabric feels great against the skin and the cut is just right for cycling, with plenty of length in the arms and body. The neck is cut to be an effective barrier against the cold air but it doesn't ever feel restrictive. 

X-Bionic Energy Accumulator V2.1 Turtle Neck - neck.jpg

It's simple to care for, too: just bung it in the wash at 40°C and it's as good as new. As with anything woven, you need to make sure that you're not lobbing your Velcro-covered gloves in the same load.

It's expensive, no doubt about that. I'm sure there are plenty of people thinking, 'I could go to [insert budget retail experience] and get a baselayer for [insert single-digit price], you wouldn't catch me paying 80 quid for a baselayer'. Yes. Yes, you could. It wouldn't be as good as this X-Bionic one. And this X-Bionic one isn't by any measurable metric 10 times as good as the £8 one you got from wherever. Such is the nature of things, and diminishing returns, and all that.

Would I part with £80 of my own money for one? Certainly I'd consider it. The performance is good enough to warrant it.


Best-in-class performance from a top-dollar baselayer

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Make and model: X-Bionic Energy Accumulator V2.1

Size tested: L/XL, Black/Orange

Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?

X-Bionic says: "WARMS WHEN YOU'RE COLD. COOLS WHEN YOU SWEAT. The cooling effect of X-BIONIC® Underwear is only activated once you start sweating. Its clever regulation system works with the most reliable of starters: your sweat. One-of-a-kind and effective, with its cooling power always exactly when you need it. Regulates your personal micro-climate, developed by scientists, proven by endurance athletes. You know that unpleasent feeling of being sweaty, then breaking out in goose bumps. Your body is sounding the alarm: Warning, threat of overcooling! X-BIONIC® Underwear prevents these chills. If no sweat is present, then a unique process uses air heated by the body asthermal insulation."

Tell us some more about the technical aspects of the product?

Technical composition:

94% Skin NODOR®

4% Elastane

2% Mythlan™

Material composition:

94% Polyamide

4% Elastane

2% Polypropylene

Rate the product for quality of construction:

Super-complicated technical baselayer with all sorts of stuff going on.

Rate the product for performance:

Hard to fault: really comfortable and excellent moisture control and temperature regulation.

Rate the product for durability:

Repeated washing brings it up good as new.

Rate the product for fit:

Compression fit is snug and the cut is good.

Rate the product for sizing:

L/XL size fits me very well.

Rate the product for weight:

Just right for cold weather riding.

Rate the product for comfort:

Hard to fault.

Rate the product for value:

Tough call: £82 is a big outlay for a baselayer. But it's a really good baselayer.

How easy is the product to care for? How did it respond to being washed?

Just lob it in a standard wash.

Tell us how the product performed overall when used for its designed purpose


Tell us what you particularly liked about the product

Comfort, performance.

Tell us what you particularly disliked about the product


Did you enjoy using the product? Yes

Would you consider buying the product? Yes

Would you recommend the product to a friend? Yes

Use this box to explain your score

For performance alone this might warrant a 10, it really is a fantastic baselayer. You can't ignore the fact that it's expensive though.

Overall rating: 9/10

About the tester

Age: 43  Height: 189cm  Weight: 92kg

I usually ride: whatever I'm testing...  My best bike is: Kinesis Tripster ATR, Kinesis Aithein

I've been riding for: Over 20 years  I ride: Every day  I would class myself as: Experienced

I regularly do the following types of riding: road racing, time trialling, cyclo-cross, commuting, club rides, sportives, general fitness riding, fixed/singlespeed, mountain biking, Mountain Bike Bog Snorkelling, track

Dave is a founding father of, having previously worked on Cycling Plus and What Mountain Bike magazines back in the day. He also writes about e-bikes for our sister publication ebiketips. He's won three mountain bike bog snorkelling World Championships, and races at the back of the third cats.

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