Big Agnes Mystic UL 15 Review – 850 DownTek Sleeping Bag

This Big Agnes Mystic UL 15 review is about the new 2019 version of the top-notch ultralight 3-season sleeping bag with an excellent 850 DownTek insulation.

Key features

What this is about

This is a technical sleeping bag that has been around for a few years already, but here you have the new 2019 version. You will recognize it easily because:

• it has a uniform color all over the top area (see the picture above), and
• it is with the logo of the manufacturer, visible in the picture.

The previous version is with a cross-pattern in a dark blue color on the top area, and the Big Agnes name is there instead of the logo. I am stressing this because both versions are on the market.

This text is about the 15-degree version, but you might want to know that they have the 0-degree version as well. The manufacturer describes it as a rectangular shaped bag but I see it more as a relaxed mummy-cut, you will see below the numbers for the girth, the differences between the shoulder and knee area are substantial. Note that it is built in three sizes.

Overview of the most important features

The insulation

The insulation is the most important part here. So you have a cozy 850 fill power DownTek water repellent insulation, and you will rarely find a bag with a higher fill number, though it may go to 950. They use a PFC-free, Bluesign-approved chemistry. So each plume is covered with an anti-bacterial and anti-microbial finish. If it gets wet, it will dry faster than ordinary down, this is what the manufacturer claims.

Flex-Pad Sleeve

Note that the bottom is lightly insulated. This is on purpose because when pressed by the body, this insulation does not work in any case, at least this is what theory says. But I have seen people complaining that the bag is not warm enough because of this asymmetric insulation distribution.

In any case, they have designed the bag with a stretchy pad sleeve. To have a proper overall insulation, you have to use a properly rated pad as well to match the bag, this is probably the reason for some of the complaints. You lose far more body warmth to the ground than to the air, up to 50 times more, dependent on the ground. This is why it is essential to have a sleeping pad with a good R-value. See the bottom with a pad in place:

In the specifications below, you will see the size of the pad that fits the sleeve, it is different for different sizes of the bag. Note that having such a sleeve is a great option for those who turn a lot during the night, I am one of them. The pad in the sleeve keeps the bag and you in place and also prevents the bag from twisting around your body. This is simply an excellent addition in general, you have it in some other bags on the market of course. Here is the side view with the pad in the sleeve:

The fabric & zippers

You have a very durable nylon ripstop shell fabric with a water-repellent finish. The lining is a nylon taffeta and the construction is what they describe as Insotect Flow. My understanding is that this implies that the movement of insulation is minimized inside the baffles.

The bag is equipped with an anti-snag YKK #5 zipper for a smooth, quick zip. This is the top brand in the zippers industry, just to know. The length of the zipper is:

• Small: 60 in (152 cm).
• Regular: 65 in (165 cm).
• Long: 70 in (178 cm).

They build this sleeping bag with zippers on either side, so you can choose what suits you best. So you can mate together left and right zip bags and have a double size to use with your partner.

Other features

• Small mesh inner pocket.
• The insulated jacket-style hood has an inner pillow pocket.
• Cordlock is available to close the hood around the face.
• No-draft collar.
• No-draft zipper.
• Interior fabric loops for sleeping bag liners.
• Exterior loops for hang drying or storage.
• Mesh storage sack included.

Who is it for

Size-wise, it is available in three sizes small (S), regular (R), and long (L). You will see below the meaning of these sizes expressed in numbers. Basically, this means it is a unisex model and you can choose the size the suits you best and avoid carrying unnecessary weight. Note that both S and R sizes are quite short.

Weight-wise, with its 2 lb (907 g) for the size R, this is an ultra-lightweight bag suitable for backpackers and hikers. But this also means it is suitable for anybody. It is also incredibly packable because of such a high-quality fill, but this only assuming that you have an appropriate compression sack, it is not included with the bag, pity.

Seasons-wise & climate-wise, the temperature rating is such that this is a 3-season sleeping bag. Note that it has no ventilation features which you can find in some Nemo’s bags so it may be too warm for summer camping.

Here is a short video with this Mystic and Blackburn sleeping bags presented by the brand:

Specifications

• Sizes: S, R, L.
• Temp rating: 15 F (-9 C).
• Fill: 850 DownTek.
• Weight:
  – S: 1 lb 13 oz (822 g).
  – R: 2 lb (907 g).
  – L: 2 lb 5 oz (1.05 kg).
• Fill weight:
  – S: 13 oz (369 g).
  – R: 14 oz (397 g).
  – L: 16 oz (454 g).
• Possible compressed size (no compression stuff sack included):
  – S: 6 x 5 in (15 x 13 cm).
  – R: 7 x 6 in (18 x 15 cm).
  – L: 8 x 7 in (20 x 18 cm).
• Actual packed size: 17.5 x 8 in (45 x 20 cm).
• Girth (shoulders/hips/knees):
  – S: 63/57/43 in (160/145/109 cm).
  – R: 69/60/49 in (175/152/125cm).
  – L: 72/63/52 in (183/160/132 cm).
• Fits:
  – S: 5’5″ (165 cm).
  – R: 5’10” (178 cm).
  – L: 6’6″ (198 cm).
• Needs pad:
  – S: 20-25 x 66 in (51 x 168 cm).
  – R: 20-25 x 72 in (51 x 183 cm).
  – L: 20-25 x 78 in (51 x 198 cm).

Big Agnes Mystic UL 15 bag vs Competitors

In the table below I show this bag side by side with two other top-notch Nemo bags with the same temperature rating. Observe that the Mystic 15 is much lighter although it is a very relaxed mummy bag, and this is due to i) a better down fill and ii) far less fill in the bottom of the bag. But those Nemo bags have some extra features like Thermo Gills, vents on the chest area. Please follow the links for more.

Final thoughts, rating, pros & cons

The included stuff sack is quite ordinary without compression straps and such a packed size is far from impressive. The indicated packed size below is only if you use such a separate compression stuff sack. In view of its price, this is so disappointing.

The price depends on the size but this is an expensive and high-end item. Please see how I rate it against the same criteria used for all the bags here in the site:

Big Agnes Mystic UL 15

9.4

Weight

8.8/10

Packed size

10.0/10

Temperature rating

9.6/10

Comfort & features

9.2/10

Pros

• Great temperature rating.
• Quality fill.
• Quality materials.
• Useful pad sleeve.
• Three sizes to choose from.

Cons

• Very expensive.
• No compression straps on the carry bag.

If you would rather have a synthetic insulation bag, check their Big Agnes Bolten SL 20 Degree Sleeping Bag, but such insulation, although top quality again, is heavier than 850 down.

For more options and different top brands, please check my page with sleeping bags, you have some excellent models there presented in detail.

Note that I am not paid by the manufacturer and this is not a sponsored text. There is a comment box below so please use it and share your thoughts. Have a nice day and pleasant backpacking.