The truth about breathable fabrics

Linen is breathable. Cotton is breathable. Wool is warm. Polyester makes you sweat.

We hear these things so often that they start to sound like facts carved in stone.

But fabric is rarely that simple.

A fabric's fibre tells us what it is made from. It doesn't tell us everything about how it will feel against your skin, how it will behave in humid weather, how much air will move through it or whether you'll still want to be wearing it six hours after you put it on.

That's something I've learned to pay much more attention to as I've spent more time choosing fabrics and making clothes.

When I'm choosing a fabric for an Unbound garment, I'm not simply asking whether it's made from linen or cotton or viscose. I'm asking a much more useful question:

How is this fabric going to behave?

Will it allow air to move? Will it absorb moisture? Will it dry quickly? Will it cling to the body? Will it drape or hold its shape? Will it feel cool when you first put it on but become uncomfortable as the day gets warmer?

And perhaps most importantly: will I actually want to wear this garment?

What do we mean by breathable?

“Breathable” is one of those words we use all the time without necessarily stopping to define it.

At its simplest, a breathable fabric allows air and moisture to move through it rather than trapping heat and humidity next to your skin.

But there are several things happening here.

Air permeability describes how easily air can pass through a fabric. A loose, open fabric will generally allow more air movement than a dense, tightly woven one.

Moisture management is about what happens when your body produces sweat. Does the fabric absorb some of that moisture? Does it spread it across the surface? Does it allow it to evaporate?

And then there is thermal comfort: that wonderfully subjective thing that determines whether you think a garment feels cool, comfortable, clammy, sticky or suffocating.

These things are related, but they're not identical.

That's why simply looking at the fibre content on a fabric label doesn't give you the whole story.

Fibre is only part of the story

Imagine two fabrics. Both are 100% cotton. One is a lightweight, loosely woven cotton voile. The other is a dense cotton canvas. They're made from exactly the same fibre, but you wouldn't expect them to behave in the same way.

The voile is light, open and airy. Air can move through it easily. The canvas is dense, substantial and designed to withstand considerably more wear.

The difference isn't the fibre. It's the fabric construction.

The same principle applies to linen, viscose, silk, polyester and pretty much every other fibre. When a fibre is spun into yarn and turned into fabric, it becomes part of a much bigger equation.

The fibre matters. But so do:

• the thickness of the yarn
• how tightly the yarns are packed together
• the weave or knit
• the weight of the finished fabric
• the fabric's surface and finish
• how much the fabric drapes or clings
• whether it has been blended with another fibre

This is why I've become wary of statements like “linen is breathable” when they're presented as though that tells us everything we need to know.

Linen can be breathable. But what kind of linen?

A little fabric experiment

Here's something you can try the next time you're fabric shopping, and you don't need any specialist equipment.

Take two or three fabrics, ideally made from different fibres. Hold each one up to the light. Can you see light clearly through it? Is the structure quite open or does the fabric look dense and compact?

The fabric on the left is a silk/cotton blend voile I used to line my daughter's formal dress. It has a loose weave, is lightweight and allows a lot of air and light to pass through. The fabric on the right is the midweight polyester satin I used for the main dress. It is tightly woven, opaque with a high sheen.

Now hold the fabric loosely over your hand. How does it fall? Does it collapse softly around your hand, or does it hold its shape?

Finally, bring it close to your skin. Notice the sensation. Does it feel cool? Dry? Smooth? Crisp? Slippery? Fuzzy?

None of these observations will give you a scientific measurement of breathability. But they will start teaching you something much more useful as a sewist:

how to look at fabric rather than simply reading the label.

We'll come back to this idea throughout this series.

So, are natural fibres more breathable?

Generally, many natural fibres are excellent choices for warm-weather clothing.

Linen and cotton are familiar examples. Wool can be surprisingly good at regulating temperature. Silk has a reputation for being comfortable in warm conditions.

But I don't think the useful conclusion is:

Natural = breathable.

And I definitely don't think the opposite is:

Synthetic = bad.

It's more complicated than that.

Natural fibres have different structures and characteristics. Synthetic fibres can be engineered to behave in particular ways. And once a fibre becomes a finished fabric, its construction can dramatically change how it performs.

This is also where we need to be careful with another common category: plant-based fibres. A fabric can start with a plant and still not be a natural fibre in the conventional textile sense. That's where fibres such as viscose, rayon and lyocell enter the story.

We'll get much deeper into those in later articles, because the world of regenerated cellulose fibres is fascinating, and full of terminology that can make your fabric label look considerably more complicated than it needs to be.

What about polyester?

Polyester gets a particularly bad reputation when we talk about breathable clothing. And there are good reasons why some polyester garments can feel hot and clammy, particularly in warm, humid conditions.

But again, “polyester” doesn't describe one single type of fabric. A dense polyester satin, a lightweight sports fabric and a sheer polyester chiffon are obviously going to behave very differently. Synthetic fibres can also be engineered to transport moisture, dry quickly or allow air to move through the fabric.

So rather than writing polyester off completely, I'd ask a better question:

What is this particular polyester fabric designed to do?

That's a much more useful question when you're standing in front of a fabric rack. It also reminds us that every fabric choice involves trade-offs. Polyester can offer durability, strength, easy care and quick drying. Those properties can be extremely useful.

But if I'm choosing a fabric for an everyday summer garment where comfort, natural hand feel and breathability are the priorities, I may make a different choice. That's not because polyester is inherently “bad”. It's because it's not the right tool for that particular job.

Weight matters too

One of the easiest mistakes to make when choosing summer fabric is to assume that lightweight automatically means breathable. It often helps, but it isn't the whole story.

A very lightweight fabric can still have a dense construction. Conversely, a slightly heavier fabric with a relatively open construction may allow plenty of air movement.

And then there's the question of opacity. The more open and lightweight a fabric becomes, the more likely you are to encounter issues with transparency, durability or the need for a lining.

This is why fabric selection is always a balancing act.

You might want something:

• light

• breathable

• opaque

• durable

• fluid

• crease-resistant

• easy to sew

• easy to care for

You may not get all of those things in one fabric. And that's fine.

Both of these fabrics are satin but I chose each of them for different reasons. The orange satin on the left is a viscose satin I used to make a bias cut skirt for a friend who lives in the same humid climate as me. Comfort and airflow were her key concerns. The plum satin on the right is a heavier, polyester satin I used to make a formal dress for my daughter. For her, appearances were paramount and this satin was excellent at resisting wrinkles. Plus, her event was going to be in an air-conditioned venue.

Breathability isn't the same in every climate

This is particularly noticeable in a place like Australia. A fabric that feels wonderfully cool on a dry summer day can behave quite differently when the temperature rises and the humidity goes with it. When the air is humid, there is less opportunity for moisture on your skin or in your clothing to evaporate. That's one reason a fabric can feel perfectly comfortable in one environment and sticky and unpleasant in another.

So when you're choosing fabric, don't just ask:

"Is this a summer fabric?"

Instead, ask:

"What kind of summer?"

A hot, dry climate?

A hot, humid climate?

A day spent outside?

An air-conditioned office?

A warm evening?

A garment that will be worn loose over the body, or something much closer fitting?

The “best” fabric can change with the answer.

And then there are blends

Blended fabrics are sometimes treated as though they're a compromise. I don't see them that way at all. On the contrary, blending fibres can be a very clever way of combining useful characteristics.

Linen and cotton can bring together some of the characteristics of both fibres. Linen and viscose can create a fabric with the character of linen but a softer, more fluid drape. Cotton blended with elastane can add stretch and comfort. Wool and silk can combine warmth, softness and strength.

A blend isn't automatically better than a single-fibre fabric. It's simply another set of choices and trade-offs. And this is something I think is worth remembering whenever you see a fabric label:

The question isn't “How natural is this fabric?”

The better question is “What does this combination of fibres and construction achieve?”

My fabric rule of thumb

I don't think there is one perfect fabric.

There are fabrics that are right for a particular garment, a particular climate and a particular person.

That's why the fabrics I choose for Unbound tend to be lightweight to midweight woven fabrics with a focus on linen, linen blends, cotton and regenerated cellulose fibres such as viscose and lyocell.

I'm looking for fabrics that feel good against the skin, allow movement, suit everyday life and have characteristics that will make the finished garment something you actually want to wear.

And I'm interested in what happens beyond the first impression.

• How does the fabric behave after washing?
• Does it soften?
• Does it become more beautiful with wear?
• Does it wrinkle?
• Does it hold its shape?
• Does it still feel good at the end of a long day?

Those things matter just as much to me as the fibre written on the label.

Because ultimately, fabric isn't just a material specification. It's what your clothes are made of and what your clothes feel like to live in.

Try this next time you buy fabric

Before you buy your next piece of fabric, resist the temptation to look at the fibre composition first. Instead, pick it up. Feel it. Hold it to the light. Scrunch it in your hand. Let it fall over your arm. Hold it against your skin.

Ask yourself:

"What is this fabric trying to do?"

Then look at the label and see whether the fibre composition helps explain what you've just experienced. You might be surprised by what you discover.

And once you start looking at fabric this way, shopping for it becomes much more interesting.