When it comes to staying warm in the great outdoors, some people prefer down insulation. Other people prefer synthetic insulation. In reality, both have pros and cons. If you’re not sure which type of insulation to choose, don’t worry. This guide is designed to help you select an insulation material that works best for your needs.

Down Insulation

Benefits of Down Insulation

Contrary to popular belief, down insulation is not made of feathers. Down is actually the fluffy undercoating that provides warmth for geese, ducks and other waterfowl. The structure of down provides warmth by creating thousands of tiny air pockets. It’s also breathable, which allows unwanted moisture vapor to escape. Ounce for ounce, down is warmer than nearly all synthetic insulations. Very few manmade fibers can match down’s warmth-to-weight ratio. Down retains its shape and loft well. With proper care, it can last for decades. Few synthetics can beat down's longevity. Down is also highly compressible and lightweight. Although synthetic insulation has come a long way, it still doesn't hold a candle to down's ultralight weight and amazing compressibility.

Disadvantages of Down Insulation

Unlike synthetic fibers, down loses its insulating power when it becomes wet and takes a long time to dry out, especially in a humid climates. Cleaning down gear requires special care. Only very mild detergents or down-specific cleaning products should be used. Although it’s not a problem for many people, down is not hypoallergenic. Although the down may not cause an allergic reaction itself, lower quality down can harbor dust particles, debris or other non-down materials, causing a reaction in sensitive people. However, high-quality down is cleaned very well according to strict industry standards, and is less likely to cause an issue. If you're prone to allergies, invest in only high-quality down products, or go with synthetic. Just keep in mind that products with down insulation are typically more expensive than products with synthetic fill.

Types of Down Insulation

High-loft goose down is made from the finest down and provides the highest warmth-to-weight ratio of any natural or synthetic insulation. It is also the most expensive insulation material.
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.

Down Fill Power Explained

Down is rated according to fill power, which is directly related to the loft quality. Fill power is represented by the number of cubic inches one ounce of down will occupy. For example, if one ounce of down takes up a volume of 650 cubic inches, it is given a 650 fill power rating. The quality of the down is directly related to its fill power rating. Thus, down warmth is a function of both fill power and the amount of fill in a sleeping bag or garment. High-quality down has a high fill power and is much loftier than down of a lower quality, requiring fewer ounces of down to create the same level of warmth, and therefore weighs less. Most outdoor gear and apparel companies use only goose down, which has a minimum fill power of 500 to 550. Goose down fill power can go as high as 800. The higher the fill power, the better the down will insulate, because there is less chance of cold spots forming (spots where the down has shifted away, leaving an uninsulated area). If a label doesn't specify fill power, it is usually because the down falls in a range below 400 cubic inches or the item contains less than 75% down.

Down Grades

Down also comes in a number of different grades. For example, a 90% goose down garment will consist of 90% down and 10% feathers (small parts of feathers that were not separated from the down during the manufacturing process). The higher the percentage of down, the better the warmth-to-weight ratio will be, and the higher the cost.

Synthetic Insulation

Benefits of Synthetic Insulation

Synthetic insulation has become much more sophisticated in recent years. There are now numerous types of high-performance synthetic insulations available, and several come close to down in terms of warmth-to-weight ratio. Synthetic insulation is essentially polyester threading that is molded into long, single threads or short staples to mimic down clusters. Thinner and lighter threads fill voids and trap warm air more effectively. Meanwhile, thicker strands sustain loft and durability. Unlike down, synthetic insulation is water-resistant and will still provide some warmth if it gets wet. Most synthetic fills are, at the very least, resistant to moisture. Some will even repel water. Synthetic insulation also dries much faster than down. If you’re on a budget, synthetic insulation will usually keep you warm for less money. It’s also easier to care for. Most synthetic fill sleeping bags or garments are machine washable and dryable. Most synthetics are also completely hypoallergenic and will not cause allergies, as long as you keep them clean.

Disadvantages of Synthetic Insulation

Synthetic insulation is heavier and bulkier than down, requiring more weight and volume to keep you in the comfort zone. A 30-degree down sleeping bag will always pack down smaller and weigh less than a 30-degree synthetic bag. Synthetic fibers gradually break down no matter how well you care for them. You may find yourself replacing synthetic products more often compared to down products.

Common Synthetic Fills

Polarguard® is an insulating material made of continuous synthetic fibers. It retains its loft and insulating properties when wet. It is also non-allergenic, mildew-resistant, machine washable and drier-friendly. Polarguard® 3D is made of a softer fiber that more closely resembles down. Polarguard® HV is made of continuous synthetic fibers, but is 25% lighter and more compressible. Polarguard® Delta is constructed of hollow-core continuous filaments that are lighter, more durable and more thermally efficient.
Primaloft® is an ultra-fine microfiber blend that is incredibly soft, lightweight, and water-repellent. It also has a down-like softness that adds comfort. In addition to sleeping bags and outerwear, Primaloft® is also used to make winter footwear. Primaloft® One has the highest warmth-to-weight ratio of any synthetic insulation currently on the market. It’s soft, durable, high-loft and made from 100% polyester microfiber. It’s also lightweight, compressible, fast-drying and water-resistant.
Thinsulate® was introduced as the original "warmth without bulk" synthetic insulation. Even wet, it is still quite warm. The breathable, ultra-fine microfibers trap warm air more efficiently than larger, generic synthetic fibers. Thinsulate® comes in 40, 70, 100, and 150 gram weights. The higher the gram weight, the warmer the insulation.
Thermolite® insulation provides an excellent warmth-to-weight ratio, even when wet. It’s also machine washable and dryable. Thermolite® Extreme is engineered to provide the most warmth per weight and durability of any Thermolite® variant. Thermolite® Extra most closely resembles the warmth, softness and fullness of down. Thermolite® Micro is less bulky, but provides excellent softness and warmth. It’s also the most compactible. Thermolite® Plus is designed for use in extreme conditions and is the most water resistant.
Dryloft® is a two-ply laminated shell fabric designed specifically for insulating parkas and sleeping bags. Dryloft® is twice as breathable as Gore-Tex®, but not as waterproof.
Hollofil® is a basic polyester insulation used in some sleeping bags and apparel.
Liteloft® is a polyester and olefin blend used in sleeping bags and outerwear.
Quallofil® high-loft polyester insulation has a soft, down-like feel. It’s used primarily in sleeping bags.
MicroLoft® is a polyester insulation made of fibers thinner than a human hair. The dense structure traps heat more efficiently than most basic synthetics of equal thickness. It’s also highly water resistant.

Thermoloft® medium-loft synthetic insulation combines solid-core polyester fibers with hollow Quallofil® fibers.

Down vs. Synthetic: The Final Word

Wrapping Things Up

Can we declare a winner in the down vs. synthetic debate? Like many things in life, one is not strictly better than the other in all circumstances. Two decades ago, down was clearly the better overall option. As technology has improved, however, synthetic has made significant headway. In order to find your best match, keep these points in mind: Down insulation works well for just about everyone, unless you frequently find yourself in extremely wet conditions or you’re on a budget. Down has the highest warmth-to-weight ratio, and is the least bulky. Synthetic insulation is better in wet conditions, and is easier to clean. It’s also a good choice for casual outdoor enthusiasts who only use their gear a handful of times a year and for people who prefer to save money.