B'Twin's 700 Ultralight Gilet is my favourite bit of kit at the moment. It comes with me on virtually every ride thanks to its light weight and packability.
Ultralight is bang on as you can barely feel this gilet when it's in your hands let alone on your back. The 100% polyester fabric is very thin which keeps the weight down to just 60g for the large size. It's fully windproof and does offer a degree of water resistance against drizzle and fog.

You don't get a mesh back to disperse heat like you see on a lot of gilets but there are two armpit vents which do a pretty good job of stopping you getting too clammy.
The cut is pretty form fitting with no excess fabric flapping about in the wind. An elastic hem keeps things in place when you're on the bike. It's got a good high neck too. The full length zip is covered by a small tab to stop neck irritation.

At the rear is a neat little drawstring pocket which'll hold a phone and an energy bar. On the other hand you can stuff the gilet into it when you've finished wearing it. You can be pretty rough with the Ultralight when ramming it in there making it easier to put away while in the saddle. The whole package ends up the size of your palm and easily fits into a jersey pocket.
White is the only option but its very tastefully done with just a few small logos dotted around. Road spray washes off fine and I didn't have any issues with staining over the test period.

In use the Ultralight is amazing at keeping the wind out for such a thin fabric and the wind on your arms is more noticeable due to the fact that the BTwin is blocking it completely from your torso. The neck keeps the drafts out to front and back.
It's comfortable, moving with you well on the bike although you do get that scrunching noise that afflicts all polyester items and a large amount of static which thankfully is more noticeable when you are putting the gilet on or off.
Overall
For a penny under twenty quid the Ultralight is pretty amazing. Not only does it perform well and look smart but BTwin back it all up with a two year warranty. Looking at the construction though I don't think you're going to need it.
Verdict
Smart looking, great performing stowaway gilet that's hard to beat in terms of value for money
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road.cc test report
Make and model: BTwin Ultralight Bike Gilet 700
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?
A windproof gilet that is ideal for aspects of cycling in cool and windy conditions. Both of which the Ultralight deals with very well.
Tell us some more about the technical aspects of the product?
100% polyester
windproof
water resistant
60g
S - XXL
Rate the product for quality of construction:
8/10
Rate the product for performance:
9/10
Rate the product for durability:
8/10
Rate the product for weight, if applicable:
9/10
Rate the product for comfort, if applicable:
8/10
Rate the product for value:
9/10
Tell us how the product performed overall when used for its designed purpose
Very well indeed, its windproof and packs down very small
Tell us what you particularly liked about the product
The windproofing.
Tell us what you particularly disliked about the product
The static build up.
Did you enjoy using the product? Yes.
Would you consider buying the product? Yes.
Would you recommend the product to a friend? Yes.
Age: 35 Height: 180cm Weight: 76kg
I usually ride: Whatever needs testing or Genesis Flyer, fixed of course! My best bike is: Kinesis T2 with full Centaur Red
I've been riding for: 10-20 years I ride: Every day I would class myself as: Expert
I regularly do the following types of riding: time trialling, commuting, club rides, sportives, fixed/singlespeed,
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