Duvet Fill Power & Warmth Guide: Down vs Wool vs Silk Free Reference Chart

Compiled by Down Under Bedding, a Canadian natural-bedding maker in business since 1989. Free to reference and link to — no email required.

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What Fill Power Actually Means

Fill power is a lab measurement: the number of cubic inches that one ounce of down clusters occupy when fully lofted. It is a proxy for the size and quality of the down clusters, not a direct warmth rating. Two duvets can have the same fill power and different warmth if they use different total fill weights — a duvet's actual warmth comes from the combination of fill power and total ounces of fill used (baffle box construction also matters, since it stops the fill from shifting and creating cold spots).

Down vs Wool vs Silk: Full Comparison

Matching Fill to Climate

Consistently cold winters: a high fill-power goose down duvet (700+) gives maximum warmth without heavy weight.

Variable or shoulder-season climates: Australian wool adapts automatically as room temperature shifts through the night, so one duvet covers more of the year.

Hot sleepers or warm climates: mulberry silk is the coolest natural fill — it wicks moisture rather than trapping it.

Couples with mismatched temperature needs: wool is the most forgiving single-duvet option since it regulates individually rather than committing to one temperature profile.

Frequently Asked Questions

Is higher fill power always warmer? Not by itself — it means more loft (air-trapping capacity) per ounce, so it's more efficient at converting fill weight into warmth. A duvet's total warmth depends on both fill power and how many ounces of fill are used.

What fill power is considered luxury or hotel-grade? 800 and above is generally considered luxury/hotel-grade; 850 is close to the practical ceiling for goose down.

Which fill is best for allergies? All three — properly processed goose down, Australian wool, and mulberry silk — are naturally hypoallergenic and dust-mite resistant. Wool and silk have a slight edge since they need no special washing to achieve this.

Can I use a wool or silk duvet in winter? Yes. Wool actively regulates toward warmth in cold conditions, and silk retains enough warmth for indoor winter use in most climates; if you want maximum winter warmth specifically, a high fill-power down duvet will outperform both.

Does fill power affect price? Yes — higher fill power requires more mature, higher-quality down clusters, which cost more to source, so price generally rises with fill power at a given fill weight.