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Therm-a-Rest MondoKing 3D Review

Our favorite option if you need a narrower comfy pad.
Therm-a-Rest MondoKing 3D
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Price:  $210 List | $209.95 at REI
Compare prices at 2 resellers
Pros:  Warm, comfortable, fits in a smaller tent
Cons:  Heavy
Manufacturer:   Therm-a-rest
By Maggie Brandenburg ⋅ Senior Review Editor  ⋅  Sep 6, 2019
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#4 of 15
  • Comfort - 40% 9
  • Ease of Use - 20% 7
  • Warmth - 20% 10
  • Versatility - 10% 7
  • Packed Size - 10% 6

Our Verdict

The Therm-a-Rest MondoKing 3D Large is a large, self-inflating mattress and a top performer for comfort and size. Featuring four plush inches of cushy foam, this mattress does a stellar job insulating you from the cold ground while supporting your pressure points and making you wish your bed at home was this nice. Though it doesn't pack down as small as some other camping mattresses, its astonishing comfort and tent-friendly width make it an excellent choice for a weekend at a music festival or a family reunion in the woods. If you're looking to pair intense comfort with smart inflated dimensions, this is the camping mattress for you.

Product Updated

The MondoKing 3D was updated since our testing period; details below.

November 2019

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Our Analysis and Test Results

Updates to the MondoKing 3D

Therm-a-Rest graced this camp mattress with some updates since we tested it. There is a new stretch-knit fabric, which is designed to be cozier and more breathable. The pad now his a ridged pattern, thanks to the new StrataCore construction. And finally, Therm-a-Rest gave this mattress a new valve. The TwinLock valve has two one-way valves for ease of inflation and deflation, which are claimed to be three and five times faster, respectively. The new MondoKing 3D is shown in the first photo, followed by the previous model we tested.

Therm-a-Rest MondoKing 3D

The updated MondoKing retails for a bit more than its predecessor. We are linking to the updated model above.

Performance Comparison

When we set out to review camping mattresses, we knew it would be challenging to tease out how they stacked up next to each other). To find out, we put these mattresses through a myriad of tests. The MondoKing 3D performed as well as many of the other camping mattresses in this review,


Compared to your standard inflatable sleeping pad or basic air mattress, using the Therm-a-Rest MondoKing 3D is bonafide luxury camping. Vertical sidewalls mean that you can utilize the entire 25-inch width and 77-inch length to spread out and sleep like a king among starfish. If you feel like you need an even larger sleeping space, the TMondoKing 3D also comes in size XXL, which is 30 inches wide and 80 inches long. While it's always great to have options, read on to learn why we think the MondoKing 3D in Large might be a better size for your life.

The MondoKing boasts an impressive four-inch foam core and can be adjusted in firmness with a few breaths pushed in or let out. This flexibility allows the MondoKing 3D to accommodate all kinds of sleepers, whether you've got back pain, you're a side or stomach sleeper, or even if you sleep with your 70lb dog. However, our reviewers found that this mattress was challenging to deflate to your comfort level simply by lying on it with one of the two-way valves open. The air-filled foam inside was so rigid that we had to get up and fold down the end to let out as much air as we wanted to make it fit our comfort needs. While this wasn't our ideal way of adjusting the air level in a mattress, it seemed a minor inconvenience when compared to the comfort and support of the MondoKing.

The soft polyester surface of this mattress provides a non-slippery, non-plastic-y plane that you can comfortably lay your cheek on without worry of sticking uncomfortably in warm weather. While we found this mattress to be very comfortable, it lacks the conforming, memory foam-like feel of some of the other foam mattresses we reviewed.

Ease of Use

We had heard that the MondoKing 3D takes a REALLY long time to inflate the first time you get it out of the box, and we found that to be true. Our reviewers were able to speed up the initial inflation a bit by adding periodic breaths over several hours, but we would not recommend taking this product camping without first having fully inflated it at home at least once.

After the initial inflation, however, we were impressed with how quickly this self-inflating mattress goes from stored in its stuff sack to fully inflated and ready to cradle you to sleep. Though this mattress does not come with a pump, our reviewers never found themselves wishing they had one — the two two-way valves are designed and located so that you can easily get them to your mouth and bite them to add a couple of quick breaths, and the impressive self-inflating capacity of the MondoKing means you don't have to huff and puff to top this mattress off. Within five minutes of starting the inflation process, the MondoKing was ready to soothe us into dreamland.

The MondoKing 3D comes with easy-to-follow deflation instructions that help make the most of having two valves for deflation. However, being full of foam, the MondoKing requires a significant amount of bodyweight to really squeeze all that air out — making it something of a process to get this mattress back into its storage sack. By following the directions included with the MondoKing and using our entire body weight (plus a little extra bouncing!), we were able to fit it back in its storage bag. It is a little bit more challenging to roll down tightly if you forget that the two-way valves mean you have to close them between rolling iterations to prevent the mattress from inflating again.

We found the MondoKing was easy in inflate, rather finicky to deflate and fit back in its bag, and the bag very convenient to carry and store.


The R-value says it all when it comes to the warmth of the MondoKing 3D. R-value tells you the insulating power of any given sleeping pad or camping mattress, giving you an idea of how cold of a surface you could comfortably sleep on without that coldness seeping through to your body. To winter camp, it's generally recommended that you use a sleeping pad or mattress with an R-value of at least 4. Coming in with an astonishing R-value of 11.4, the MondoKing is well-equipped to insulate you from the frozen ground and maybe even from an iceberg! It's also just as important to note that unlike the cold-temperature rating of a sleeping bag, having a camping mattress with an R-value, this high won't make you pour sweat in hot weather. This is a solid four-season camping mattress.


Based on the overall size and weight of the MondoKing 3D, this isn't the camping pad you would take on a backpacking trip. You're not going to want to carry this mattress too far from your car or garage. However, as a full 5 inches narrower than most of its competitors, the MondoKing has a few advantages.

Your average two-person tent is around 50-55 inches wide. This means that if you're using a 30-inch wide camping pad you can only fit ONE camping pad into your TWO person tent. However, by using the well-performing MondoKing 3D Large, you can fit TWO of them side-by-side inside a two-person tent, as the tent rating suggests. While we suggest you check this against your own personal tent width, as tent styles and sizes may vary, you're much more likely to be able to fit the promised number of people in your tent by using the MondoKing 3D Large than most of its competitors from this review.

Packed Size

When packing the car for a weekend of camping, the MondoKing isn't too large to leave behind, and more than makes up for its size with its comfort. While we wouldn't be stoked to pile seven of them in the back of the van, the space it takes up is pretty comparable to the other highly comfort-rated mattresses in this review. And while the internet led us to believe that we could pack this mattress back down into a nice little 7 by 26-inch package, we found that very challenging to achieve.


The MondoKing 3D is on the more expensive side of the self-inflating camping mattresses we tested. Despite being a decent chunk of change to throw down on a camping mattress, we think you'll find the comfort and versatility of the MondoKing 3D Large to be well worth the dough.


This pad combines a high level of comfort compared to all the camping mattresses we reviewed, with a slightly narrower width to fit more easily into the tent you already own. The MondoKing 3D is an excellent all-around camping solution, and we would happily recommend it to both our dirtbag, live-out-of-my-van friends as well as our hard-to-please, princess-and-the-pea family members.

Maggie Brandenburg