Best 40-Degree Sleeping Bags

Updated October 2021
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BestReviews spends thousands of hours researching, analyzing, and testing products to recommend the best picks for most consumers. We buy all products with our own funds, and we never accept free products from manufacturers.Read more 
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How we decided

We purchase every product we review with our own funds — we never accept anything from product manufacturers.

54 Models Considered
8 Hours Researched
2 Experts Interviewed
93 Consumers Consulted
Zero products received from manufacturers.

We purchase every product we review with our own funds — we never accept anything from product manufacturers.

Buying guide for best 40-degree sleeping bags

Gearing up for your next camping trip? Even if you’re heading out in comfortable weather, you’ll need plenty of warmth when the temperature plunges at night. Adding a 40-degree sleeping bag to your camping gear is essential to staying warm and cozy while you sleep.

Forty-degree sleeping bags are considered summer or low-elevation sleeping bags because they’re designed with multiple layers of insulation to regulate temperature. To prevent overheating, many designs adjust to warmer temperatures by means of removable sections or hoods. Some convertible designs are fully expandable and open up to become a cozy comforter. In addition to all their comfort and warmth features, 40-degree sleeping bags also come in three shapes: mummy, rectangular, and semi-rectangular.

Which sleeping bag is best for you? It’s time to hunker down and bundle up for a new excursion. Read our 40-degree sleeping bag buying guide to find the perfect choice for your next cool night outside.

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Take care and go slow when using the zippers on your bag to avoid catching the liner and potentially ripping it.

Key considerations

Understanding 40-degree sleeping bags

Forty-degree sleeping bags are summer bags. Their insulation and warmth is relatively modest. These bags are intended to keep sleepers comfortable during the overnight temperature drop. A sleeping bag’s temperature rating is based on nighttime temperatures, which can vary considerably, especially at higher altitudes.

The goal of a 40-degree sleeping bag is temperature regulation — retaining heat when there’s a chill and venting heat on warmer nights. This versatility is achieved by using lightweight materials and employing convertible design options such as removable hoods and vented foot boxes.

Shapes

Forty-degree sleeping bags are available in three basic shapes: mummy, rectangular, and semi-rectangular.

Mummy bags bundle you up, leaving only your face exposed. Many campers joke that they look just like baby swaddles, and it’s actually an accurate description. With that said, mummy bags offer superior coverage, especially with a hood, but most don’t actually compress your body like a baby swaddle does. They’re ideal if you like a snug bag and don’t want to bother with layering clothing while you sleep.

Rectangular bags usually have a simple design: open at the top with a zipper down one side. Certain styles also have foot boxes that open, which usually means the bag can open up like a quilt. Rectangular bags are a no-fuss, easy-roll-up option.

Semi-rectangular sleeping bags typically borrow the body of a rectangular bag and the head of a mummy bag. These bags often feature a removable hood or head section. Semi-rectangular bags provide a bit more head coverage and cushioning without going full mummy.

Features

Weight

Since you’re probably packing light for a camping trip, it’s no surprise that 40-degree bags are designed to be as lightweight as possible. Some weigh less than two pounds, though others can weigh up to four pounds. If you’re backpacking, a couple of pounds will feel like a big difference.

Materials

Most 40-degree sleeping bags are made of polyester but the grade and quality of the fabric varies. You’ll need to consider both the thickness and the thread count of the polyester.

Thread count: The thread count measures how much many threads are used horizontally and vertically per square inch. A high thread count means the weave is tighter, so it retains heat better and is usually more comfortable. As an example, a 350 thread-count polyester is more tightly woven and of higher quality than 250 thread-count polyester.

Denier: The thickness and weight of the polyester thread used to manufacture sleeping bag material is measured by its denier scale rating, often denoted by a “D” after a number. Higher denier numbers represent thicker and more durable construction; items with lower denier numbers will be softer and silkier.

Insulation

Sleeping bags are typically insulated with down or synthetic fiber filling. Down lasts much longer than synthetic options. Synthetic fill is much cheaper and lightweight but tends to become matted and lumpy over time.

When comparing bags, pay attention to the grams per square meter (GSM) of filling. The higher the number, the denser the filling. Go for a high GSM if you want a bag that is as thick or fluffy as a puffer jacket, but if you’re looking for something more compact and lightweight, opt for a sleeping bag with a lower GSM.

Closures

For the most part, 40-degree sleeping bags have zipper closures. Some bags, especially mummy styles, also feature drawstrings around the face area if you’d like to really bundle up.

There are also some bags with closure redundancy to truly seal it off, which often includes an extra flap that snaps closed over zippers. Some bags are equipped with draft guards, which are placed behind the closed zippers instead. Velcro-closure zipper covers are also featured on some bags.

40-degree sleeping bag prices

For the most part, you’ll find 40-degree sleeping bags for $20 to $80. While price depends on the quality of insulation and design, choosing a sleeping bag from a brand name generally means you’ll be paying a premium.

Inexpensive: For $20 to $30, expect to find mostly rectangular sleeping bags with decent quality and lightweight insulation. There are also a large number of kids’ bags in this price range.

Mid-range: If you spend between $30 and $60, you’ll find sleeping bags in all three shapes. Many of these bags are convertible as well, so regulating your sleeping temperature and comfort is easier.

Expensive: For a high-end 40-degree sleeping bag, expect to spend between $60 and $80. These sleeping bags have superior construction and better linings. This price bracket also includes some all-weather bags that excel at temperature regulation.

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Tips

  • Try more than one bag. Yes, get inside more than one sleeping bag to see which shape and insulation style you prefer.
  • Consider the temperature. A 40-degree sleeping bag is ideal for temperate conditions, but it’s not recommended for use in temperatures below 40°. For camping in colder conditions, you’ll need a sleeping bag with a lower cold-rating number.
  • Shake out your bag. Before you get into a sleeping bag, always shake it out to remove dust, dirt, and any creepy crawlies that may have nestled inside.
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If you’re taking an RV trip and don’t want to lug a large bag of bedding, bring your sleeping bags instead. You won’t need to make beds or clean sheets after the trip.

FAQ

Q. How long will a 40-degree sleeping bag last?
A.
It depends on the insulation as well as the quality. Down sleeping bags can last up to ten years or more, whereas bags with synthetic filling can be worn out in two or three years. It also depends on how often you use the sleeping bag. If a bag is used only a couple of times a year, it should last for a decade or more.
 

Q. How do I clean a sleeping bag?
A. Camping experts say it’s best to avoid dry cleaners and to simply soak and hand wash your bag yourself. Fill up a tub of lukewarm water and add some gentle detergent that is appropriate for filling and insulation. Let the bag soak for up to an hour. Drain the tub, thoroughly rinse out the bag, and let it hang dry. It can take a few hours to dry thoroughly, but be sure to do so. Stowing a sleeping bag that’s not completely dry can cause mold or mildew.
 

Q. Can I get an adult bag for a kid?
A.
You can, but they might miss out on the warmth of a well-fitted sleeping bag. Some styles, especially mummy bags, are designed with an ultra-insulated foot box. If a child’s feet can’t reach it, they won’t be able to take advantage of the feature — which is definitely important on colder nights.
 

Q. Are sleeping bags waterproof?
A.
No, but they may be water-resistant. If you prefer a sleeping bag that can handle a spill without getting soaked, choose one with a higher thread count. Small amounts of water will typically bead off the bag, but if you spill a large amount, it will become saturated. Another option is to spray your sleeping bag with a fine coat of waterproof spray — but check with the manufacturer to determine whether the bag can handle this type of waterproofing treatment.

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