Warmer, gram for gram: HeatLock™ AERO vs. down

How aerogel spun into the fiber compares with 90% white duck down, measured on the same test plate.

Down has been the benchmark for lightweight warmth for as long as people have made insulated jackets, and it has earned that. So when we built a sample jacket filled with HeatLock® AERO, down was the obvious thing to test it against.

We sent fill panels to the Guangzhou Inspection Testing and Certification Group (GTTC), an independent laboratory, for a direct comparison. Both panels used the same shell fabric and the same weight of fill. The only difference was what was inside.

The setup

GB/T 35762-2017 is China’s national flat-plate test for heat transfer through textiles. The sample lies on a heated plate held at a steady temperature, and instruments measure how much power the plate needs to stay warm. The more heat the insulation holds back, the less power the plate draws. It is a controlled, repeatable way to answer one question: how well does this material stop heat from escaping?

The results

At the same 200 g fill weight, the HeatLock® AERO panel had about 43% more thermal resistance than the down panel.

All four measurements point the same way, and they check against each other: thermal resistance and the heat transfer coefficient are reciprocals, and the reported values agree.

What the numbers mean

Thermal resistance measures how strongly a material resists heat flowing through it. Higher is warmer.

Clo says the same thing in terms people can picture. One clo is roughly the insulation of a business suit — enough to keep someone sitting still comfortable at about 21 °C (70 °F). One clo equals 0.155 m²·K/W, so 0.741 ÷ 0.155 gives 4.78 clo. The HeatLock® AERO panel returned about 1.4 clo more than down from the same weight of fill.

Heat transfer coefficient is the other side of the same coin: watts passing through each square metre for each degree of temperature difference. HeatLock® AERO let through 1.35 W against down’s 1.94 W, about 30% less heat lost.

Warmth retention rate compares the plate’s heat loss with the sample in place against its loss with nothing on it. 88.5% against 85.1% looks close until you look at the heat that got through: 11.5% for HeatLock® AERO, 14.9% for down — roughly 23% less heat escaping.

Why aerogel in the fiber makes a difference

All insulation works by trapping still air. Heat leaves a jacket three ways:

1. Conduction, through the fibers themselves and through the air held between them
2. Convection, as air moves through the fill
3. Radiation, as infrared energy crosses the gaps

Down is very good at trapping air, because its clusters spread into a large, springy loft. Ordinary polyester fill traps air too, but the fibers are solid polymer, and solid polymer carries heat.

HeatLock® AERO changes the fiber itself. Silica aerogel is one of the lightest solids ever made and one of the poorest at carrying heat. It is mostly air, held in a network of pores only nanometres across. Those pores are smaller than the distance an air molecule normally travels before striking another, so the molecules cannot pass heat along the way they do in open air. The result is a material that conducts heat less well than the still air inside it.

We add the aerogel to the polymer during melt spinning, before the fiber is formed. It becomes part of the fiber rather than a coating on its surface, so it cannot wash off, flake off or wear away. That is the idea behind every Meridian fiber technology: it’s in the fiber.

What this test does and does not show

• It compares equal weights. Both panels held 200 g of fill in the same shell, and the result applies to that setup.
• It is a panel test, not a wear test. The flat plate measures the insulation. How warm a finished garment feels also depends on fit, baffles, seams and how it is worn.
• It was run dry. Synthetic fills are known to hold loft better than down when wet or compressed. We have not yet put numbers on that for HeatLock® AERO. It is the next test.
• It covers one grade of down. Our comparison was 90% white duck down, a common commercial grade. Higher fill-power down would perform differently.

What this means for product teams

At the same fill weight, HeatLock® AERO measured substantially warmer than down in an independent laboratory. That gives a designer two moves: keep the weight and gain warmth, or keep the warmth and cut weight and bulk. It is also a synthetic fill, with the supply chain traceability that comes with it, and the fiber is certified to OEKO-TEX® STANDARD 100.

HeatLock® AERO is supplied as staple fiber for fill and padding, with padding from 60 to 200 g/m².

See it at the show. We will have the sample jacket and fiber samples at our booth this October at the Functional Fabric Fair in Oregon. Full GTTC test reports are available on request.