Down Jacket Fill Power Guide for Nepal Trekking (2026)

What Is Down Fill Power and Why Does It Matter in Nepal?

If you're buying a down jacket for a Nepal trek, the single most misunderstood spec is "fill power" — and getting it right is the difference between a warm, packable jacket and a heavy, bulky one that lets you down at altitude. Fill power measures the loft (fluffiness) of down: specifically, how many cubic inches one ounce of down expands to fill. A higher number means more warm air trapped per gram, so more warmth for less weight. On a trek where you add and remove your jacket dozens of times a day and every gram in your pack counts, that efficiency is gold.

But fill power is only half the story. This guide explains both fill power and fill weight, and tells you exactly which combination you need for each Nepal trek.

Fill Power Explained: 650 vs 800 vs 900

As a rule of thumb, about 1.31 oz of 650 fill down provides the same loft as 1.0 oz of 850 fill down — so higher fill power gives the same warmth at lower weight and smaller packed size.

Why Fill Weight Matters As Much As Fill Power

Here's the trap many trekkers fall into: a high fill-power number alone doesn't make a jacket warm. Fill weight — the actual grams of down inside — determines total warmth.

• A 650 FP jacket with 330g of down is roughly as warm as an 800 FP jacket with 120g of down
• The 800 FP jacket will be lighter and pack smaller for that same warmth
• For real cold (EBC, Gokyo), you want both high fill power AND high fill weight (e.g. 800 FP / 250–350g)

Always check both numbers, not just the headline fill power.

Which Fill Power Do You Need for Your Nepal Trek?

• Poon Hill / Mardi Himal / Langtang / ABC: 650–700 FP, 150–250g fill
• EBC / Gokyo / Manaslu: 800–850 FP, 250–350g fill
• Three Passes / winter EBC / Island Peak: 850–900 FP, 350g+ fill (expedition class)

See our full down jacket range matched to each trek.

Goose Down vs Duck Down, and Hydrophobic Treatment

• Goose down: Typically reaches higher fill powers (800+); slightly warmer for weight
• Duck down: More affordable; excellent up to ~700 FP; the practical choice for most trekkers
• Hydrophobic/DWR-treated down: Repels moisture and retains loft in Nepal's humid pre-monsoon spring — well worth it

Reference Jackets and What to Look For

• Look for an insulated hood, hip-length cut, and a baffled (not stitch-through) construction for cold treks
• Packability into its own pocket is essential — you'll stow it constantly
• Quality benchmarks include the Patagonia Down Sweater (800 FP), Rab Microlight (700 FP), and Rab Neutrino Pro (800 FP) class
• Combine your down jacket with a fleece and a waterproof shell for a complete layering system

Frequently Asked Questions

What fill power down jacket do I need for Everest Base Camp?

For EBC trekking (not climbing), a jacket with 700+ fill power is recommended for the coldest nights. For daytime use and active trekking, a 550–650 fill power packable jacket works well combined with a hardshell.

Is 650 fill power down warm enough for Nepal?

650 fill power is warm enough for moderate-altitude treks like Poon Hill, Mardi Himal, Langtang, and ABC — provided it has enough fill weight (200g+). For high-altitude treks like EBC or Gokyo, step up to 800 FP.

What's the difference between 650 and 800 fill power?

800 fill power down lofts more per gram, so an 800 FP jacket is lighter and packs smaller than a 650 FP jacket of equal warmth. About 1.31 oz of 650 fill equals 1.0 oz of 850 fill in loft.

Is goose down better than duck down for trekking?

Goose down typically reaches higher fill powers and is marginally warmer for its weight, but quality duck down up to 700 FP performs excellently and costs less — making it the practical choice for most Nepal trekkers.