What is fill power in a duvet insert?

Fill power measures how much space a given weight of down occupies when it lofts. Higher fill power means larger, loftier down clusters that trap more air, providing better insulation for less weight.

What fill power range is best for South African homes?

For most South African homes, a 600-700 fill power duvet insert is a good balance of loft and cost. In milder coastal areas, 500-600 fill power works well, while colder highveld nights may benefit from 700-800+ fill power for a warm, light duvet.

How does fill power differ from fill weight?

Fill power is the quality of down (fluffiness per gram), while fill weight is the total amount of down inside the duvet. Both numbers together determine warmth; a high fill power with low fill weight can be cooler than a lower fill power with high fill weight.

Does higher fill power always mean a warmer duvet?

Not necessarily. Warmth depends on both fill power and fill weight, as well as construction and shell fabric. A high fill power duvet with a small fill weight may be less warm than a moderate fill power duvet with a higher fill weight.

What should I look for when comparing duvet inserts by fill power?

Look for both fill power and fill weight on the product page. Check the down percentage, look for testing certifications like IDFL, and consider a baffle-box construction to prevent cold spots. These details make fill power meaningful.

Duvet insert fill power guide: how fill power affects warmth, weight and value

Understand duvet insert fill power, how tests work, and how to pair fill power with fill weight and construction for South African bedrooms.

Published:May 18, 2026

Updated:September 9, 2026

5 min read

Photo by Sincerely Media on Unsplash

What fill power is - explained simply

Fill power is a standard measure of how much space a given weight of down occupies when it’s allowed to loft. In everyday terms, higher fill power means larger, loftier down clusters that trap more air per gram. That trapped air is what gives a duvet insert its insulating ability: more air equals more warmth for less weight.

How the test works

Laboratories measure fill power by placing a fixed weight of treated down into a graduated cylinder and recording the volume it fills when allowed to loft under controlled conditions. That volume becomes the fill power number (for example, 500, 700 or 800). The test is repeatable, which makes fill power useful as a comparative figure between down products.

Fill power versus fill weight

Two duvets can use the same fill power but feel different because of fill weight - the total amount of down inside. Think of fill power as quality (fluffiness per gram) and fill weight as quantity (how much down). To understand how warm a duvet will be, consider both numbers together rather than fill power alone.

Choosing a fill power range for South African homes

South African bedrooms vary - from coastal, milder climates to colder highveld nights - so there’s no single best fill power. As a rule of thumb:

500-600 fill power: good value, slightly heavier for the warmth, works well for everyday all-season duvet inserts.
600-700 fill power: a sweet spot for lighter but warm inserts; good for most homes that want a balance of loft and cost.
700-800+ fill power: premium, very lofty down that delivers high warmth-to-weight ratios; useful if you want a light, lofty winter duvet without extra weight.

Keep in mind these bands are general guidance. The way a duvet feels also depends on construction (baffle-box vs sewn-through), shell fabric, and your bedroom's insulation or heating.

If you prefer to try options, we often start with a mid-range 600-700 fill power insert and add layers or a topper in colder months. For shoppers looking specifically for duvet inners, we suggest browsing our Duvet Inners & Pillows selection on the site: Duvet Inners & Pillows.

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Practical tips: what to look for when you shop

When we compare duvet inserts, these checklist items help make fill power meaningful in real life:

Ask for both fill power and fill weight - a 700 fill power with tiny fill weight will be cooler than a 600 fill power with heavy fill weight.
Check the down percentage: higher down-to-feather ratios usually give a cleaner loft and feel.
Look for reputable testing or certification (lab tests, IDFL reports) when available - these back up fill power claims.
Consider construction: baffle-box chambers help the down loft evenly and prevent cold spots.

How fill power affects cost and value

Higher fill power down is more expensive because it uses larger, higher-quality clusters. In South Africa, expect estimated price bands for a single duvet insert (estimates only): a basic down/feather insert might start around R500-R1 200; mid-range 600-700 fill power inserts often sit in the R1 200-R3 000 band; and premium 700-800+ options can be R3 000 and above depending on size and brand. These are broad ranges and vary by retailer and seasonal offers; use them as planning estimates.

When fill power matters most

Fill power matters when we want high warmth with low weight - for example, a lightweight winter duvet for a draught-free bedroom, or when we prefer a lofty hotel-style feel without extra heaviness. For warm bedrooms or people who sleep hot, fill power is less important than selecting a lower tog or combining layers that breathe.

Quick tip: Match fill power to how you sleep - if you like a light, fluffy cover and have colder nights, choose higher fill power with moderate fill weight. If you like weight and warmth together, moderate fill power with higher fill weight works well.

Final checklist before you buy

Confirm fill power number and fill weight (grams) on the product page.
Note down-to-feather ratio and any cleaning or care instructions.
Compare construction (baffle-box for better loft) and shell fabric (tighter weaves prevent down leakage).
Consider our local climate and whether you’ll use a single duvet year-round or combine two for winter and summer.

If you want more practical reading on bedroom bedding and seasonal choices, check our Bed & Linen articles for local guidance: Bed & Linen articles.

Sources

REI - What Is Down Fill Power? (practical explanation and examples)
IDFL - Fill Power: Questions & Answers (laboratory testing details)
Fill power - Wikipedia (overview of measurement and implications)
Patagonia - Down Fill Power Explained (useful context on warmth vs weight)

We hope this duvet insert fill power guide helps you choose with confidence. When you’re ready to shop or compare sizes and materials, our Duvet Inners & Pillows shop and Bed & Linen articles are easy places to start exploring options that suit your room and budget.

Last updated: September 9, 2026

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Duvet insert fill power guide: how fill power affects warmth, weight and value

Why Choose Bash?

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Why Choose Bash?

Free Delivery

30-Day Returns

Nationwide Support

What fill power means

Use fill power + weight

Local buying tips

What fill power is - explained simply

How the test works

Fill power versus fill weight

Choosing a fill power range for South African homes

Practical tips: what to look for when you shop

How fill power affects cost and value

When fill power matters most

Final checklist before you buy

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