Columbia Reactor 35 Mummy



This is a great low-price synthetic bag for summer…

Rating: rated 4 of 5 stars
Source: bought it new
Price Paid: ~$80


This is a great low-price synthetic bag for summer and early fall hiking. The "Omni-Heat" reflective dots do a great job of capturing body heat while the "Omni-Shield" 30D nylon shell blocks wind. A nearly full-length double zipper allows you to quickly and easily adjust the bag for optimum comfort in varying weather.


  • Inexpensive
  • Captures body heat
  • Good wind resistance
  • Good weather resistance
  • 3/4-length zipper


  • Bulkier than a down bag
  • Temperature varies dramatically by person
  • No mattress pad attachment points
  • Zipper pulls on outside only

I originally picked up the Columbia Reactor 35 as a backup bag when the airline lost my pack and we weren't certain we'd be able to intercept it on our way into the woods. In the end, this bag turned out to be quite welcome as it was more comfortable than the bag I was carrying at that time and provided an extra layer on one particularly chilly evening.


MATERIALS:  The Reactor 35 is made primarily of 30D nylon ("Omni-Shield" shell) and polyester (lining / insulation) with the addition of small metallic dots. These dots (called "Omni-Heat" by Columbia) are the same as what you would find in an emergency blanket. The one big difference is that, instead of being one solid sheet, "Omni-Heat" mounts these dots on a polyester fabric. This provides warmth without sacrificing breathability (more on breathability later).

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Since all materials are synthetic, this bag can be stored compressed (unlike a down bag), but will not compress nearly as much as a down bag would. It can also be washed without fear of damaging the insulation and creating cold spots in the bag.  

DESIGN:  The Reactor 35 has a standard mummy shape for optimal warmth retention. It has a 3/4-length zipper that runs down the side of the bag from the footbox to the hood where it terminates with a small velcro flap.  The hood itself has a drawstring closure that can be cinched tight for colder nights. The bag also has a small exterior pocket just below the hood. It isn't large enough for much, but fits a headlamp nicely for those late-night bathroom runs.


SIZE:  The Reactor comes in regular and long lengths. They say the regular size fits people up to 6' which seems to be pretty accurate as it was just too short for me. The large size easily accommodates someone between 6'2" and 6'5".  

You may have a little bit of trouble if you have particularly broad chest / shoulders. I wear a 42" jacket and found the Reactor to be quite snug around the shoulders. This wasn't an issue on most nights as I left the zipper partially open, but was a little uncomfortable when fully zipped for warmth.


ENTRY AND EXIT:  The 3/4-length zipper makes entry and exit pretty easy. The velcro at the head of the zipper makes it even easier. Most nights, I would leave the zipper about 3/4 zipped and then fasten the velcro. This would hold the bag around me for warmth, but would still allow me to reach out and quickly undo the zipper when I wanted to get out.

The one issue I had with entry and exit on this bag is that the zipper pulls are on the outside of the zipper only. You can still somewhat operate the zippers from the inside, but there was much more contortion involved in fully sealing the bag than I was used to.


WARMTH:  Due to the inclusion of the "Omni-Heat" reflective lining, this bag is less reliant on loft for warmth than other bags. With a fill weight of 16oz, this bag is actually pretty sparsely insulated for my taste. The "Omni-Heat" does a great job of capturing body heat (almost too well sometimes), but it is highly dependent upon the user's body heat.  

If you're a cold sleeper, a few jumping jacks before bed will really help make this bag more comfortable. Once inside the bag, the "Omni-Heat" does a great job of capturing body heat while a ~2" wide insulated baffle covers the inside of the zipper to protect against drafts.


On various trips, I have found that this is a great bag for tents and a terrible option for hammocks. The "Omni-Heat" does a great job trapping body heat, but the lack of loft means it won't do much about breezes under your hammock. While using a hammock, I always had this bag cinched up as tight as possible to try and capture as much heat as a could.  While in a tent, I actually found that I could usually keep it halfway or completely unzipped.

If you wish to use this bag with an air mattress, make sure to keep your air mattress inside the bag itself (There are no attachment points for mattress straps on the outside of this bag). Something like the Klymit Inertia X Frame would be a good choice for this bag as it will help to insulate you from the ground, but will still allow the "Omni-Heat" lining to reflect body heat back to you.

BREATHABILITY:  While emergency blankets leave you absolutely drenched, the "Omni-Heat" has pretty decent breathability. This is because they only use small metallic dots on a polyester fabric sheet. You don't get quite the same warmth you would from an emergency blanket, but you do get far better breathability. However, once temperatures started to rise, I quickly found the inside of my bag getting damp with trapped sweat.

PACKABILITY:  This bag is actually pretty compact for a fully synthetic 35F bag with a full-length zipper. This comes back to the fact that Columbia was able to minimize the amount of insulation by including their "Omni-Heat" foil lining. While the stuff sac itself is 16.5" x 7.5", the bag only takes up about 14" x 7.5" and, using the compression straps, you can get it down to about 12" x 8".

There are synthetic bags out there that will beat this, but most of them do so by getting rid of critical components such as the 3/4-length zipper. A half-length or quarter-length zipper will definitely make the bag easier to pack, but it also makes it more difficult to get in and out and dramatically reduces the usable temperature range.  

As for weight, the Reactor 35 comes in at 41.92 oz (about 2.6 lbs). Given my current 20F quilt comes in at just 20.47oz, it's hard to see why I would like a bag with a higher temperature rating that weighs more than twice that. The reason is price.

My current quilt came in at $375 while the Reactor 35 came in at just $80 when I bought it at Bass Pro Shops. If you're willing to pay the money for a good bag / quilt, you'll immediately notice warmth and quality differences, but this is a great backup bag. I used mine on 2 or 3 trips then made it my loaner bag for group canoeing / hiking trips.  

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Great review of a really nice looking bag, Brent! I really like the idea of adding a pocket on the bag. I have a few questions. How does the bag feel against your skin? Is it sticky or anything? Is it noisy? You have been working hard on some awesome reviews lately. Keep up the great work! :)

28 days ago
Brent Mills

Hey Ashleigh. It's actually a very comfortable fabric. It feels about the same as any other polyester or 20D / 30D nylon fabric. I actually had a jacket made of this material for a few years and really liked it. It does crinkle a little bit, but not enough that it ever bothered me. One thing to note is that the foil dots wear down over time (we're talking 2-3 years of daily use here), so the fabric loses some heat retention over time, but also becomes quieter and softer over time.

28 days ago
Kevin Sweere

Good review.

26 days ago
Kevin Sweere

Good review... but nitpick on the SCIENCE. Reflective materials are more about marketing than warmth. Radiant heat loss/gain is is related to the temperature difference (to the fourth power) and emissivity between objects. The temp delta between the inner bag's layer and your pajamas is near zero, thus no benefit. If you're sleeping outside under clear skies, in theory you'd be warmer wearing it inside out (space temp ~ -40F, bad temp ~ air temp means a large delta). Same applies to foil emergency blankets.

26 days ago

Good to know, Brent. Thanks for the answers! :)

26 days ago

Lightweight and highly compressible bag. I have used…

Rating: rated 4.5 of 5 stars
Source: bought it new
Price Paid: $160


Lightweight and highly compressible bag.


  • Packs very small.
  • Water resistant (Omni-Shield)
  • Warms up fast (Omni-Heat)
  • Accurate temperature rating (at least for warm sleepers like me)
  • Lightweight
  • Nice zipper
  • Nice construction
  • Very reasonably priced


  • No loops for sleeping pad straps

I have used the bag down to 30°F and was warm wearing my UA Coldgear long sleeve and pants. I've slept in it in a t-shirt and underwear down to around 35°F.  There weren't any cold spots or drafts and the bag warms up very quickly with the Omni-heat lining, which I expected to be a gimmick.  

I'm 6-1 and the regular size bag fits me perfectly. Plenty of room in the shoulders and I can comfortable lay without touching either end of the bag, but close. Easy to get in and out of, the zipper is "snag-proof".  

The Omni-shield makes the bag water resistant, which works great for nights with heavy condensation if you use a single walled tent like I do. The bag compresses to be very small and weighs only 2lbs. The fabric it is made of seems very delicate, but my 70 lb catahoula moves around and sleeps on my legs at night and it doesn't even have a snag or hole anywhere from his nails after at least a dozen nights.

Columbia Reactor 35 Mummy

previously retailed for:
$69.73 - $159.00

The Columbia Reactor 35 Mummy is not available from the stores we monitor. It was last seen March 27, 2015 at REI.

If you're looking for a new warm weather synthetic sleeping bag, check out the best reviewed current models.