This does not come with a battery. It runs off a USB power bank you supply, and two things matter — the first one catches people out.

Output power decides whether it turns on at all. Output in watts is voltage times current, so 5V × 2A is 10W and 5V × 4.5A is 22.5W. Below 10W it may not start. At 18W or more you get the full range of settings, and the higher settings actually feel higher. If you already own a power bank, check the small print on the back before you order.

Capacity decides how long it runs. As a rough guide, a 10,000 mAh bank gives a few hours on the higher setting and longer on the lower ones. A 20,000 mAh bank roughly doubles that. These are not lab figures — how cold it is, which zones you run and whether you have a coat over the top all change it.

There is a pocket inside the lining for the bank, with the cable running to it. A 20,000 mAh bank is noticeably heavier than a 10,000 — worth thinking about if you will be moving around in it.

These run small. Most people need to go up one or two sizes from what they
normally wear in the UK.

The most reliable way to get it right: take a gilet or jacket you already own, lay it flat, measure across the chest and double it. Match that number to the column below — that is how these are measured at the factory, so it is a like-for-like comparison.

Size      Garment chest    Shoulder    Length
M          104 cm            39 cm        62 cm
L           108 cm            40.5 cm     64 cm
XL        112 cm            42 cm        66 cm
2XL      116 cm            43.5 cm     68 cm
3XL      120 cm            45 cm        70 cm
4XL      124 cm            46 cm        72 cm

Measured by hand, so allow a centimetre or two either way. If you are between two sizes, take the larger one — it is meant to go over a jumper, not against your skin.

It is cut as a men's gilet, but plenty of women wear it. Go by the chest measurement, not the label.

Three areas: the collar and back of your neck, across your back, and low at the front.

The heating elements are panels. They are not the whole surface of the gilet — so you feel warm areas spreading out, not an even glow everywhere. The neck and the back are the strongest; the front is gentler.

Front and back run on separate buttons, each with three settings. You can have the back on and the front off, or the other way round.

It is warm, not hot. A steady warmth rather than a radiator. It works best as a mid-layer, with a coat over the top — the coat holds the heat against you. Worn on its own in the wind, a lot of it goes straight out. The gilet itself is thin, and that is the point: it is built to go under something.

It is also noticeably warmer than a plain gilet with the heating switched off, just from the lining.

Heated areas      Collar and back of the neck, across the back, low at the front
Controls             Front and back on separate buttons, 3 settings each
Time to warm      About 1 to 2 minutes
Power                USB power bank, not included — 10W minimum, 18W or more recommended
Cable                Built in, runs to an internal pocket
Shell                 100% polyester
Lining                100% polyester
Collar                Turn-down, heated panel at the back of the neck
Closure              Full-length zip
Pockets              Two outer, one inner for the power bank
Sizes          M to 4XL — runs small, see the size guide
to three sizes smaller than UK
Colours              Black, blue
Made in             Hubei, China

In the box
The gilet
Built-in USB cable

Not in the box
A power bank — you will need your own, see above
A printed manual — the setup steps are on this page instead

1. It is warm, not hot. If you are picturing an electric blanket you can wear outdoors, this is not that. It takes the edge off a cold day and it does that well — but it is a warm layer, not a heater.

2. It needs a coat over it to do its best work. On its own in the wind you will feel it much less. We would rather say that here than have you find out in a car park.

3. The sizing is not perfectly consistent. These are made in batches and they do not all come out identical. Measure a garment you own and compare it to the table — do not trust the label.

4. It is a £59.99 gilet, not a £160 one. The fabric is light, the inner pocket is a simple one, and a small number of these do fail. If yours does, email us and we will sort it out.

5. It is not a medical device. It does not treat, cure or manage anything. It makes a cold day easier to be outside in. That is the whole claim.

Wear it for a full month. If it is not for you, write to contact@hiluci.co.uk and we will refund it or replace it, whichever you prefer.

That is on top of your legal right to cancel within 14 days of delivery under the Consumer Contracts Regulations 2013 — the thirty days is simply us giving you longer.