The science of cosiness: a textiles expert explains feather down, bamboo, polyester duvets

As the weather cools in the southern hemisphere and energy prices climb, many of us are trying to stay warm without cranking the heating.

The doona – or duvet, if you prefer – is central to that battle.

But with shelves stocked with everything from inexpensive polyester duvets to down doonas costing thousands, what’s actually worth your money?

Fortunately, there’s solid textile science to guide you – and it’s less complicated than the marketing suggests.

It’s mostly about thickness

Here’s what most doona advertising glosses over: all doonas of the same thickness provide roughly the same warmth, regardless of filling material.

That’s because a doona’s job is simply to trap air around your body – your own body does the heating.

So no, an expensive goose down doona is not automatically “warmer” than a cheaper polyester one from a discount retailer.

Thickness equals warmth – though in practice, determining how thick a doona actually is can be surprisingly difficult, as manufacturers often don’t provide this information.

But warmth isn’t the only thing that matters.

Down and feathers

Down is the soft, fluffy clusters that grow next to a bird’s skin for insulation – distinct from the tougher outer feathers, which are heavier and less effective at trapping air.

Down creates enormous loft (thickness) with very little weight, making it feel light and airy.

Down quilts are also marketed as being highly breathable. They allow moisture (sweat) to move through the quilt relatively freely, so you’re less likely to overheat.

Well-cared-for down doonas can last decades. However, they’re an animal product, and while most commercially available down is a byproduct of the meat industry, an unknown proportion globally still comes from live-plucked birds – a practice banned in many places but not eliminated.

Conscientious shoppers can look for products certified to the Responsible Down Standard.

Down doonas are generally the most expensive available, and not all downs are the same.

The most common types are duck and goose, with goose down generally considered superior (larger down cluster, higher loft). But both are marketed similarly.

For the best quality, look for higher “fill power”, meaning the down clusters are larger and trap more air. This results in a thicker and lighter weight doona.

For the truly committed, Icelandic eiderdown (ethically collected from the nests of Eider ducks without harming the birds) represents the gold standard – but they can cost upwards of $A30,000.

Wool is a strong contender

A wool quilt is the closest natural alternative to feathers.

It doesn’t quite match down for loft, but it’s not far behind – and it brings some unique extras.

Wool absorbs volatile organic compounds (a class of indoor air contaminants). Research suggests it has a meaningful “buffering” effect on moisture, moving sweat away from your body significantly better than polyester.

Like down, however, wool is another animal product. Depending on the source of the wool, it may be a byproduct of the meat industry.

While shearing sheep is essential for the animal’s health, farming practices such as tail docking and mulesing (where flesh is cut from the lamb’s buttock area, to reduce the risk of flystrike infection) may still spark concern.

What about cotton, polyester and bamboo?

Cotton is better at moving sweat away from your body than polyester, though not quite as effective as wool. It’s also generally the easiest to care for – a solid choice for budget-conscious shoppers who still want a natural fibre.

If you sleep hot, think carefully before choosing polyester. Synthetic fibres absorb very little moisture, meaning sweat has to travel through air spaces alone, and water vapour doesn’t move efficiently through polyester materials.

The result: that cosy warmth at bedtime can turn into sweaty discomfort by 2am.

Bamboo also deserves a mention, though mostly as a caution. Bamboo-derived fibres (almost always viscose or rayon) are produced by chemically dissolving raw bamboo down to its components, then extruding it as semi-synthetic fibres. Claims that bamboo products are inherently antibacterial or uniquely eco-friendly are generally unsubstantiated – a classic case of greenwashing.

What if I’m allergic to dust mites?

One 2002 New Zealand study found higher levels of dust mite allergens in synthetic doonas and pillows compared to natural alternatives such as down and wool.

Regardless of filling, practical steps – such as putting woven fabric dust mite covers on mattresses and pillows, regular washing in warm or hot water, and tumble drying – can help reduce allergens.

The bed as a system

Whatever you choose, always read and follow the care and laundry instructions.

Look for doonas with internal “baffles,” which create separate compartments that keep filling evenly distributed even through washing.

Air regularly, use a doona cover, spot clean as needed, and if you’re uncertain about washing, take it to a dry cleaner for deeper cleans.

Adding a wool blanket between your sheet and doona (or a wool underlay on top of the mattress) can boost warmth and breathability; keeping the wool layer closest to your body is where it does its best work absorbing moisture.

Similarly, two lighter doonas layered together will likely be as warm as one thick one.

In this way, it helps to think of your bed as a system rather than focusing on the doona alone.