When the first truly chilly morning arrives, most of us stand in front of our wardrobes squeezing sweaters and wondering the same thing: which material is warmest? The answer is not the thickest garment – it is the one that holds the most air, and which continues to provide warmth even when it gets damp. This is why a thin wool sweater often beats a thick acrylic cardigan.
In this guide, we walk you through why certain fibers provide more warmth than others, how wool, fleece, down, cotton, and acrylic compare to each other, which material you should choose for which layer – and how to build an autumn wardrobe that actually keeps you warm.
Contents
- Why does a material provide warmth?
- Wool – the warmest choice
- Materials compared
- The right material for the right layer
- Three mistakes that make you cold
- How to build a warm autumn wardrobe
- Our current favorites
- Frequently asked questions
- Summary
Why does a material provide warmth?
A fabric does not provide warmth in itself. What keeps you warm is the still air trapped between the fibers – air is one of the best insulators available, as long as it doesn't move. A material that traps a lot of air per gram therefore provides more warmth than a heavy, compact fabric.
Three properties determine this:
- Crimp. Fibers that are naturally crimped, like wool, build small air pockets on their own.
- Behavior when damp. Some fibers stop providing warmth as soon as they get wet. Others continue.
- Wind resistance. All the insulation in the world won't help if the wind blows right through.
This is also the explanation for why several thin layers beat one thick one: each layer traps its own air gap.
Wool – the warmest choice
If you only remember one thing: wool provides the best warmth in a Swedish autumn climate. The fiber is naturally crimped and therefore traps a lot of air, but the crucial factor is that wool continues to provide warmth even when it is damp. That is exactly what you need in a country where autumn consists mostly of drizzle and raw air.
Wool comes in many forms, and they provide varying degrees of warmth:
- Merino wool – the finest fiber, itches the least, perfect closest to the body.
- Lambswool – soft and warming, the most common type in sweaters and cardigans.
- Mohair and alpaca – light, airy, and very warm in relation to their weight.
- Cashmere – warmest per gram, but delicate and expensive.
- Wool blend – wool with a touch of polyamide or acrylic. More durable, cheaper, slightly less warm.
A wool blend of 40–60 percent wool is usually the best compromise between warmth, price, and durability – and that is why most wool coats look the way they do. Femina has a good breakdown of the difference between pure wool and wool blends in their guide at Femina.
Materials compared
Here is how the most common autumn and winter materials compare to each other:
| Material | Warmth | Best for | Keep in mind |
|---|---|---|---|
| Wool | Highest – warms even when damp | Sweaters, cardigans, coats | Can itch – choose merino closest to the skin |
| Down | Most warmth per gram | Winter jackets | Loses all insulation when wet |
| Fleece | High, dries quickly | Mid-layer | Wind goes right through – needs a shell |
| Acrylic | Medium – imitates wool | Affordable knitwear | Breathes less, pills more easily |
| Cotton | Low | Layer closest to the skin in mild weather | Becomes cold and clammy when damp |
Note the row for cotton. It is comfortable and breathes well, but it absorbs moisture and then stops providing warmth – a cotton t-shirt closest to the skin is one of the most common reasons you feel cold despite having three layers on top.
The right material for the right layer
Each layer has its own task, and therefore its own best material:
- Base layer (transports moisture): merino wool or a thin functional material. Never cotton if you are going to be outside for a long time.
- Mid-layer (insulates): knitted wool, fleece, or mohair. This is where the warmth is created – a knitted sweater or a cardigan does the job.
- Outer layer (protects against wind and wet): densely woven wool coat, quilted jacket, or a water-repellent shell. See our guide to women's coats.
The most common mistake is throwing on a thicker outer garment when you feel cold. Usually, it is the mid-layer that is missing.
Three mistakes that make you cold
1. You choose thick instead of airy. A compact, tightly spun sweater provides less warmth than a light, airy knit of the same weight. Squeeze the garment – if it springs back, there is air in it.
2. You wear garments that are too tight. Tight-fitting layers press the air out between the fibers and remove the insulation. That is one of the reasons why turtlenecks and slightly oversized sweaters provide such good warmth.
3. You forget windproofing. Fleece and loosely knitted wool insulate excellently but do not stand up to wind. A densely woven outer garment over them makes more of a difference than another sweater underneath.
How to build a warm autumn wardrobe
You need fewer garments than you think – but they must be of the right fiber. A thin merino top to wear as a base layer, two to three knitted sweaters or cardigans in wool or a wool blend, and one densely woven outer garment will cover almost the entire Swedish autumn.
Then it is all about combining. A knitted sweater over a thin blouse creates two air gaps instead of one. A vest over a sweater warms your torso without making your arms cumbersome. And when it gets really cold, it is the outer garment that should be changed, not the number of sweaters – ELLE reviews this year's models in their guide at ELLE.
Our current favorites
Three garments that keep you warm all autumn:
- Maya – Knitted turtleneck in mohair blend – light, airy, and warmer than its weight suggests, with a soft acrylic lining against the skin.
- Elegant women's wool coat in longline model – densely woven wool that keeps the wind out and covers all the way down over the skirt.
- Women's oversized knitted sweater – the relaxed fit leaves air between the layers, which is precisely the point.
Viscose behaves like cotton in the hand but like silk in its drape, and that is precisely why it shrinks more than people expect. The fiber swells when it gets wet and loses a large portion of its strength; a viscose dress that is wrung out in the machine can lose an entire size in one wash. Wash cool, avoid the spin cycle, and hang the garment on a hanger while it is damp, and the weight will pull the creases out by itself. If the fabric looks dull after a few washes, it is usually lint from terry cloth in the same machine, not wear and tear. Properties, washing, and what viscose is suitable for in viscose.
Frequently asked questions
Which material is the warmest?
Wool, considered as the best all-around choice. Down provides more warmth per gram but stops insulating when wet, while wool continues to provide warmth even when damp – which is crucial in Swedish autumn weather.
Is acrylic as warm as wool?
No. Acrylic imitates the structure of wool and provides decent warmth in dry weather, but it breathes less and loses more warmth when it becomes damp. A wool blend is a good middle ground.
Why am I cold even though I am wearing many layers?
Usually because the layers are too tight, or because the innermost layer is cotton that has become damp. Switch to merino wool closest to the skin and leave room for air between the garments.
What is warmer – fleece or wool?
Fleece insulates very well and dries faster, but the wind goes right through it and it breathes less. Wool is the better choice when the garment is to be worn alone or as an outer layer.
Does all wool itch?
No. The itching depends on the thickness of the fiber, not on the fact that it is wool. Merino wool has such a fine fiber that it feels soft even directly against the skin.
How do I wash wool without it shrinking?
Wool cycle or hand wash at 30 degrees, wool detergent, no spin cycle, and flat drying. More on this in our guide on how to wash knitwear.
Summary
The warmest isn't the thickest – the warmest is the material that traps the most air and continues to provide warmth when it gets damp. Wool wins there, with down as a specialist for dry cold and fleece as a good mid-layer behind a windproof shell. Build in layers, leave air between them, and keep cotton away from your skin when you are going to be outside for a long time.
Ready to face the autumn? Explore our women's sweaters and coats. Free shipping within Sweden.
The material is half the answer; the other half is how you combine the garments. We have gone through the technique in the guide on layering, which shows which layer the warmth should actually be in.
Looking for something else? See all our 111 guides in a list.
