The Overquilt: Stay Warm and Protect Your Gear During Cold, Wet Nights

Washington’s shoulder seasons are fickle. One day it’s pouring rain with a high of 55 F, the next it’s bluebird skies and freezing. Conditions seem nice enough for backcountry overnights, but the seasonal environment and short days are bitter reminders that summer hikes will have to wait.

Luckily, Washington trails are beautiful year-round, so don’t let a dip in temperature drop your spirits. With the proper sleep system you can stay warm and dry, extend the life of your gear and sleep comfortably through even the roughest nights. Allow me to introduce: the overquilt.

Washington trails are great year round. Taking the proper gear can help you access even in colder months. Photo by Craig Smith

What’s an overquilt?

An overquilt, sometimes called an overbag or vaporbag, is a secondary synthetic quilt that goes over your normal sleeping bag or quilt. An overquilt must be made from synthetic insulations, or else it won’t work: more on the technical components later. Otherwise, it cinches around your sleeping pad, serving as an additional layer of warmth and protection between your sleeping bag and the exposed air. 

• Sleeping quilt? Don’t you mean sleeping bag?
• Both a sleeping bag and a sleeping quilt offer a fluffy nest to curl up inside each night, but have a few key distinctions. Learn the difference between a bag and a quilt.

Think of it like a hard shell, but for your sleeping bag. In this analogy, a sleeping bag is like a fleece and an overquilt is like a rain jacket. One specializes in keeping you warm, where the other specializes in keeping you dry.

How does it work?

To understand how it adds value to your sleep system, it’s important we know the four ways a body loses heat:

• Radiation: heat is lost through the skin
• Evaporation: heat is lost via water (sweating) and respiration
• Convection: heat is lost via wind, which carries away the warm thin layer of air adjacent to your skin
• Conduction: heat is lost via touching a colder object. In this case, the ground 

Sleeping bags, quilts and overquilts don’t combat conduction much: that’s what a good sleeping pad is for. Otherwise, overquilts do work in tandem with your sleeping bag to help prevent heat loss from radiation and convection. That second layer of the overquilt helps retain body heat and keep cold drafts out. 

Where overquilts really excel, however, is in dealing with moisture — both the moisture you lose from your body and the moisture that settles on the outside of your sleeping bag.

Water evaporated from your body and moisture from the air will accumulate on your outermost layer.

Down and synthetic sleeping layers have their pros and cons. Down materials are negatively affected by moisture (yes, even modern treated down), whereas synthetic materials withstand moisture better.

In cold temperatures moisture will attach to the nearest surface. If it’s a cold, wet night, moisture will accumulate on the outside of your sleeping bag. You’ll especially notice this if your tent has poor airflow, or if you prefer to cowboy camp. Just imagine dew settled on grass.

Similarly, your body is constantly evaporating water, even when you sleep. Normally, that water moves away from your body and into your sleeping bag. If the air outside your bag is too cold, instead of evaporating, the moisture will stay in your bag.

• My overquilt story
• I picked-up the overquilt sleep system during my 2018 thru hike attempt of the Appalachian Trail. I used my Timmermade overquilt for about 1,600 miles and 71 days — through late winter and early spring in the Appalachian Mountains — all the way from Georgia to Vermont. Between four nor’easters in March, temperatures in the teens in Tennessee and freezing rain in Virginia, the synthetic overquilt protected my Western Mountaineering sleeping bag from everything the Appalachian Trail could throw at it. I still have and use both today, together and separately, as I recreate in Washington’s shoulder seasons.

Synthetic sleeping bags are already water resistant, so this moisture doesn’t affect them much. But, for down sleeping bag users, this moisture will dampen your down sleeping layer over time. Besides permanently damaging your expensive sleeping bag or quilt, it will also diminish its ability to retain heat. That means less comfort and more work for your body when it should be at rest.

Since synthetic insulation works well when wet, an overquilt will absorb the moisture moving from your body through your down bag, plus protect your down bag from the harsh, wet air outside. Not only will you stay warmer and dryer, but your down layer will last longer overall.

When should I use an overquilt?

The overquilt sleep system is best for long trips, or a series of long trips, where you’re expecting to be in freezing temperatures with plenty of moisture. For some, this could be a series of long mountaineering traverses in the spring. For others, it could be a fall full of backpacking on the Olympic coast. For many, it might just be some added warmth on top of your regular set-up. Just remember, sleeping bag temperature ratings are rated for what temperatures you’ll survive in, not what temperature you’ll be comfortable in.

• Still not warm at night? Try these tricks:
• - Boil water before bed, then put it in a safely sealed Nalgene. Use it as a warming pan at the foot of your sleeping bag. The best part? It will be cold enough to drink in the morning!
• - Sleeping pads matter! If yours isn’t keeping you insulated, get one with a higher R-value.
• - Stuff (don’t wear) your puffy into the sleeping bag chamber next to your body for extra insulation
• - Consider a sleeping bag liner for extra warmth and to protect your sleeping bag from the dirt and oils of your body

Aim to air-out your synthetic overquilt during sunny spots of the day, if you can. This will keep it dry and ready to tackle another stormy night outside. If your sleeping layer is a quilt, some overquilts also come with a drawstring footbox, so you can air-out your sweaty feet at night as well. If you’re on a longer trip where you won’t need the overquilt the entire time, like a thru hike, you can mail your overquilt home as soon as you’re ready.

If you only go out on chilly campouts or backpacking trips one or two nights a year, you can probably get by fine with a sleeping bag rated for low temperatures, or perhaps a bivy. If you don’t have a bivy or a super powerful sleeping bag, the right overquilt can bolster your overall set-up.

Each layer supports a different part of the sleep system, but remember: your body generates heat, whereas your sleeping bag retains heat. Photo by Tynesha Campbell

A flexible sleep system: why two quilts can be better than one

Remember: a singular bag can never match the efficiency or flexibility of the overquilt system. Rather than owning a single bag rated for 10 F and using it all the time, even when it’s hot during summer, you can keep a bag rated for 20 F, plus an overquilt rated for 40 F, and use them together or separately. Sleeping bags and quilts can be expensive, so choose your sleep system wisely. We love our synthetic bags and quilts, especially in winter, but it’s helpful to consistently evaluate your gear as your recreational needs change.

Does this article make you long for warm summer nights in the mountains? Me too. In the meantime, consider putting an overquilt on your wishlist so you’ll have it ready for your next wet, cold backpacking trip. You can dream of long, sunny days (or nightmares of washing your down sleeping bag) from beneath the comfy cocoon of your insulated overquilt.