Down vs. Synthetic Insulation: How To Choose & What To Know

Humans have dedicated an enormous amount of creative energy to figuring out how to keep ourselves warm. Some of the earliest technologies we developed were ways to insulate against the cold. Insulation is material designed to prevent heat from being transmitted from one area to another.

Today, when we’re shopping for outdoor gear, we have all kinds of insulation options. There’s down insulation, Thinsulate, Primaloft, and so many more options out there. If you’re wondering what’s the difference between down insulation and synthetic insulation, look no further. We have all the information you need to understand how insulation works and to make the best choice for your outdoor activities.

 

The Science of Insulation

The fundamental principle of insulation is trapped air. When air is able to circulate, heat moves with it. Air is a mixture of gasses, and gasses on their own aren’t great at conducting heat. If you can trap air in the spaces between solids, less heat is transferred at the molecular level. Insulation actually works by removing as much solid material as possible and replacing it with tiny pockets of air.

One big pocket of air is actually less effective than lots of tiny pockets of air, and all insulation works on this principle. Big pockets of air mean that the air has room to move around and create a current. If you have a large air current, it will transfer heat from hot to cold pretty effectively. 

Once you have an air cavity more than about 1/2 inch wide, the ability for the air to circulate within the cavity starts to rise, and air becomes less effective as an insulator. So tiny pockets are the way to make insulation work!

You can look at nature to see this in action. Birds trap air in the spaces between their feathers to keep them warm. It’s how penguins are able to survive Antarctic temperatures. Animal fur works on the same principle– the air trapped between individual hairs keeps mammals warm in winter. 

 

Loft

Before we start talking about the types of insulation and comparing them to each other, we need to know what loft​​ is. For clothing insulation, the primary metric used to discuss its effectiveness is loft. Loft, sometimes referred to as fill power, is the number of cubic inches filled by an ounce of down. The higher the loft, the more effective the insulation. 

For down, the loft number is directly related to the size of the down cluster. Large down clusters trap more air and take up more space than smaller down clusters, even though they might weigh the same. Down’s cluster size is a factor of the environment; birds raised in cold environments have bigger down clusters than birds raised in warm environments. 

For synthetic insulation, the cluster sizes are determined by the manufacturing process. It is more uniform across products, but it isn’t always uniform when compared to down. For down, the loft number or fill number has a 1:1 ratio to the weight of the down. 

This isn’t always true for synthetic material, and it means that sometimes products with synthetic insulation that have the same fill number as a down product might be up to ⅓ as thin as the down product. This means that synthetic insulation can be just as warm as down, but take up less space.

 

What Is Down?

Down is the natural insulation used by birds to stay warm and dry. All birds have an undercoat of fine, fluffy feathers, but the feathers we use for down are only found on waterbirds, like ducks and geese. Down feathers have a very short shaft and don’t have the little barbules that interlock and connect the fibers of exterior feathers. The down of waterbirds is soft and thick enough to trap lots of air, which not only keeps the birds warm but also helps them stay afloat. 

 

Types Of Down

• Eiderdown is made from the collected down of wild eider ducks. It is the most expensive type of down, and only a limited amount is collected each year.  
• High-loft goose down is made from the finest down and provides the highest warmth-to-weight ratio of any natural or synthetic insulation.
• Standard goose down has slightly less loft but is more reasonably priced.
• Duck down is less fine than standard goose down and considerably less expensive.

Aside from eiderdown, the vast majority of down insulation is a byproduct of the meat industry. Down is used for duvets, sleeping bags, and outerwear. It’s a common type of insulation because it is both lightweight and effective. 

 

What Is Synthetic Insulation?

Synthetic insulation is made from polyester or other synthetic fibers and is designed to mimic the air-trapping effects of natural down. There is a greater amount of control over fiber length and loft. Synthetic insulation comes in three main forms: cluster fiber, continuous filament, and short-staple. There are also insulating fabrics that use different types of technology to preserve body heat. 

 

Types of Synthetic Insulation Fibers

• Cluster fiber insulation: numerous tiny fiber balls that closely mimic clusters of down
• Continuous filament insulation: a continuous filament that intertwines with itself to create a mass of insulating fibers.
• Short-staple insulation: tiny, short fibers that move independently

Each of these insulation types relies on trapping air, but they all do it differently. The most common type is short-staple insulation, found in all kinds of products. Some of the thinnest insulated gear, like gloves and boot liners, are made with Thinsulate® short-staple insulation. 

Cluster fiber is becoming more popular, especially since The North Face started using their proprietary ThermoBall® insulation in their jackets. Cluster fiber is excellent at keeping you warm, even when it gets wet. 

Continuous filament insulation is often found in sleeping bags or heavier jackets because it is the stiffest type of synthetic insulation. However, it has a lot of durability and loft resistance, which means that it will bounce back to its original fill after you compress it. Loft resistance can be a concern with the other types of synthetic insulation because after a lot of compression the fibers don’t always bounce back and the insulation’s performance decreases over time.

While all three main types of synthetic insulation perform well, there are some key performance differences that can help you decide what type of insulation will be best for you.

 

Synthetic Insulation Brands

Many clothing manufacturers have their own insulation brands. Some use various widely commercially available types; others use proprietary materials that are made just for them. Here are some of the most common that you’ll come across in the outdoor world. 

 

Advantages Of Down Insulation

• Breathable: Unwanted moisture can escape through down.
• Environmentally Friendly: Down breaks down and decomposes quickly when disposed of; you will also need to replace your gear less frequently if it is down-filled rather than filled with synthetic insulation.
• Lightweight: Down weighs next to nothing, and adds considerable insulation without much additional weight. 
• Loft Resistance: The tiny fibers in down always bounces back to their original shape.
• Longevity: When properly cared for, down lasts for decades. 
• Packable: Down is seemingly infinitely compressible in a way that no synthetic can match. Because down traps so much air, it can fold down to a very thin layer in your bag.

 

Disadvantages of Down Insulation

• Cleaning: Caring for down requires special detergents and care.
• Expensive: Down is easily the most expensive type of insulation. A single genuine eiderdown quilt can cost thousands of dollars; down jackets and down parkas are frequently $200 or more. 
• Non-hypoallergenic: Down is unlikely to cause an allergic reaction itself, but lower quality down can harbor dust particles and bird dander that can cause an allergic reaction in sensitive people.
• Performance When Wet: Even though down keeps waterbirds dry, it loses its insulating power when wet. Down takes a while to dry, too, so if your down jacket gets soaked on Day 1 of your week-long hiking trip, you may be facing some difficulties. 

 

Advantages of Synthetic Insulation

• Easy Care: Most synthetic insulation filled-garments and gear are machine washable and can be dried in your clothes dryer at home. 
• Hypoallergenic: All synthetic insulation types are completely hypoallergenic and will not cause an allergic reaction, as long as you keep them clean. 
• Inexpensive: Even high-quality synthetic insulation is usually cheaper than down.
• Performance When Wet: Synthetic insulation will provide warmth when wet and dries much faster than down.
• Water Resistance: Synthetics are usually at least resistant to moisture; some will even repel water. 

 

Disadvantages of Synthetic Insulation

• Cold Spots: This is not a problem with continuous fiber insulation, but short-staple insulation is prone to slipping around inside your gear. Quilting helps keep it in place, but you will need to re-fluff your gear to keep the insulation evenly distributed.
• Longevity: The fibers in synthetic insulation don’t last as long as down fibers. No matter how careful you are, you’ll find yourself needing to replace your gear as the fibers break down.
• Packability: Synthetic insulation fill doesn’t compress as flat as down does and takes up more room in your bag.
• Weight: Synthetic insulation is bulkier and heavier than down– although when considering the highest-end synthetic insulation, this gap is not large. 

 

Down Insulation Vs. Synthetic Insulation

Now that you know all the advantages and disadvantages of the different types of insulation, let’s put them head to head and see how they perform. 

 

The Final Word on Down Insulation vs Synthetic Insulation

There’s no universal answer to what type of insulation is best. Down and synthetic insulation are both high-performing insulation types, and will work great in dozens of outdoor situations. They are both different, however, and knowing their different characteristics and the reasons for these differences can help you make a truly educated choice about what kind of outdoor gear you want to buy. Both types of insulation can keep you safe and warm, and in the end, that’s what matters. We hope that this article has demystified the types of insulation and helped you figure out just what kind of insulation is best for your cold-weather adventures.