September asks the same question every morning. It is eleven degrees at eight, twenty one by one o'clock, and twelve again on the way home. A winter coat is too much, a shirt is not enough, and the jacket that actually solves it is the one most men do not own.
A transitional men's jacket is not a thin winter coat. It is a jacket you can open and close all day without the outfit underneath falling apart. This guide sorts the shapes by temperature, says what matters about the fit of each one, and finishes with the layer that goes under all of them.
What a transitional jacket has to do
Three things decide it, and warmth is not the first one.
It has to open quickly. Zip or buttons, either works, but a jacket that only functions fully on or fully off is the wrong jacket in September. The spread across a single day is around ten degrees, and the jacket has to cover both ends of it.
It has to leave room for a layer. This is the mistake that happens at the point of purchase. A jacket that fits beautifully over a T-shirt pulls across the shoulders over a knitted jumper and rides the sleeves up. Try it on over the jumper you will actually wear underneath, and you will not need to send it back.
It has to stop wind. At twelve degrees, the wind takes more heat off you than the temperature does. A windproof jacket with no lining holds warmth longer than a padded one that lets air through, which is exactly why bomber jackets with ribbed cuffs and windproof shells work so well at this time of year. They close at the neck, the hem and the wrist.
18 to 14 degrees: the Harrington, the bomber and the denim jacket
Mild days want short jackets. Short means the hem finishes at the hip and not below it. That is not a style point; it is a proportion one, because a short jacket makes the leg read longer and stays out of the way when you sit down.
The Harrington jacket and the bomber jacket are the same idea in two versions: light fabric, a zip, ribbed cuffs and hem. Both sit as well over a shirt as over a fine knit, and they are the quietest way to look dressed in September. The windproof versions are the more useful ones because they carry the evening as well as the afternoon.
The denim jacket is the other answer at this temperature and the more sociable one. It adds almost no warmth, but it blocks wind, and worn over a hoodie it does exactly what it is supposed to. One rule that makes the difference: do not wear a denim jacket with jeans in the same wash. Two different blues read as accidental, while dark chinos or corduroy trousers underneath read as deliberate.
All three shapes sit in the men's jackets collection, from lightweight zip-ups to lined bombers.
The overshirt is the jacket that is not a jacket
The overshirt, also called a shacket, is the most useful piece of this season and the least bought. It is cut like a shirt in heavier cloth, and it is worn open over whatever you already have on.
That is the whole trick. An overshirt over a T-shirt turns half an outfit into a whole one without anything underneath changing. On colder days there are fleece-lined and quilted versions, the checked flannel ones are the classics, and there is a corduroy version, which is the right surface for September anyway.
On sizing: buy an overshirt one size up from your shirt size; otherwise there is no room for the layer it exists to go over. It should finish over the trousers, never tucked in.
14 to 9 degrees: the quilted jacket
Once the mornings are in single figures, the quilted jacket takes over. It is the most sensible jacket of the whole transition because it is light, it packs down, and it still works under a coat in winter. Two things matter when you buy one.
The quilting. Narrow channels hold less warmth than deep ones, which is precisely why they are the right choice now. A thickly filled down jacket is excellent in November and too warm today.
The hood. A hooded quilted jacket covers the shower as well as the cold, and a plain collared one layers more neatly under a scarf. Both exist, and the choice comes down to whether your commute happens outdoors or mostly in a car.
The shorter answer to the same temperature is the gilet. It keeps the body warm and leaves the arms free, which on an active day is more comfortable than any jacket. Over a shirt or a chunky knit, it is the layer you do not take off at lunchtime, and the fleece and knitted versions read considerably softer than the tactical ones.
Wind and rain: fleece lined and windproof
For anything that happens outdoors, a windproof shell is the practical answer. Windproof, water resistant, and the hooded versions cover the shower that belongs to a British September. It is not a style jacket; it is a tool, and it is best used as one: the dog, the platform, the Saturday shop.
Fleece is the second half of the same answer, and it has two roles. Worn on its own, it is the soft jacket for a mild dry day. Worn under a windproof layer, it is the warmth you take out when the sun arrives. Plenty of jackets build this in with a fleece lining sewn straight into the shell, which has the advantage of being one piece to carry and the disadvantage that you cannot regulate it.
Leather and corduroy: the jackets with character
A leather jacket belongs to this season for a practical reason: leather is completely windproof. On its own it adds little warmth, but nothing gets through it, and over a fine knit at twelve degrees it is exactly right.
The biker is the shortest and hardest version, the lapel style is the softer one, and both come in faux and vegan leather. If you cannot choose between brown and black, brown combines with more, because it sits happily next to blue, green and stone. Black asks the rest of the outfit to stay quiet.
Corduroy is the civilian alternative with the same effect. Cord has the right surface for September because it holds light differently from flat cloth, which makes it read warmer than it is. The fleece-lined corduroy jackets carry you into October, and corduroy trousers are the easiest way to bring the fabric into an outfit without committing a whole jacket to it.
The coat comes later
A wool coat or a trench is almost always the wrong call in September, even though it is the best-looking thing you own. The reason is the one from the beginning: a coat cannot sensibly be worn half on. It is the right answer when the temperature drops below eight and stays there, which usually means the back half of October.
There is one exception, and it is the evening. If you are going out in a shirt, a light single-breasted coat beats a sports jacket, because it continues the line of the shirt instead of interrupting it. For everything else, the quilted jacket is the better September buy, and the coat can wait.
What goes underneath
A transitional jacket is only as good as the layer under it, and in September that layer is almost always knitwear.
A fine knitted jumper is the most reliable choice because it goes under any jacket without adding bulk. A chunky knit is warmer but wants a jacket with real shoulder room, or it pulls. The cardigan is the third option and the most flexible one, because it opens like the jacket does, which on a day with ten degrees of spread is the entire point. Put a long-sleeve tee or a button-up shirt under that, and the question is settled. The shirts sit in the polos and shirts collection, and the jumpers and cardigans run right through the full FW26 collection.
More changes below the waist than most men expect. The chinos stay, corduroy arrives, and the jeans get darker. Cord is the fabric that carries the whole season and works under every jacket named above, and it is worth checking the trousers for it before reaching for the same jeans again. Footwear can stay where it is for now: a clean white trainer under the short jackets, a leather ankle boot once the quilted jacket comes out.
If it is only going to be one jacket
For most men, the answer is the quilted jacket, because it covers the widest temperature range and survives into winter as a layer. If you spend your days outdoors, buy the windproof shell instead. And if you already own a warm coat and only need to close the September gap, buy an overshirt, because it is the cheapest way to turn clothes you already have into an outfit.
The shapes in this guide are in the jackets, the layers under them in the polos and shirts, and a scarf or a beanie for the cold mornings in the accessories. One last thing that is true every year: the jacket you buy at the end of August gets worn four weeks longer than the one you buy at the end of September. The transition starts earlier than it feels.
