Want to keep warm at night? Check out the MondoKing 3D SIM

Review Summary
A great self-inflating mat. For the large size, it's probably best for car camping.
The Good Stuff
The MondoKing 3D is a good sized Self Inflating Mat with insulation to help keep you warm on those cold nights.
The Not So Great
It is more expensive than cheaper SIMs... but you get what you pay for ;-)

Overall Rating

Value for Money


Last Updated: May 1, 2018

Therm-a-rest is a brand synonymous with great Self Inflating Mats that provide fantastic insulation.

So, naturally, I was elated when they decided to send me their MondoKing™ 3D SIM.

Therm-a-rest MondoKing 3D SIM – Large

Therm-a-rest sent over their larger version of the MondoKing 3D, which is perfect for our sort of camping, which we mainly do with the car.

As with most SIMs, the Therm-a-rest MondoKing 3D SIM has two valves at the top for inflating and deflating.

you should let it unroll at home first
I hadn’t unrolled it before taking it on our early February camp. This is not the most sensible thing to do of course, as you should let it unroll at home first, as it can take a while to inflate after being packed for so long 😉

However, after leaving it some considerable time, and giving it a few puffs of air, I had the MondoKing inflated.

A good sized SIM

Certainly, this SIM is a good size. It had plenty of room even if I rolled around a bit in my four-season sleeping bag, plus it was quite thick. Almost a few inches when inflated. (10cms is the official specs)

This is the largest Self-Inflating Mat that Therm-a-rest currently make.

Here’s how thick it ‘self-inflated’. You can, of course, make it thicker by blowing in some more air.

Another Point of View

Shell also has spent time sleeping on the MondoKing 3D.

I found the SIM to be very comfortable and plush. It didn’t feel like you were sleeping on the ground.
One of the best SIM’s I have tried. It’s also nice and quite, so it doesn’t wake you when you turn over in the night.
It’s much better than a cheap one.

Keeping me warm

The R value of this SIM is 11.4.

should be good enough down to -40C
According the specs this should be good enough down to -40C. Though I wasn’t going to test that was the case!

Using it in early February with a 4-season sleeping bag, I didn’t feel the cold, despite there being a frost outside.

I had put down poncho insulation quilt on the tent floor, so with the additional R-Value of this SIM, it was doing the job quite well.

Rolling up the Mondo King

Putting SIMs away, especially large ones, can always take a while, as a lot of air needs to get out of the valves at the top.

The Mondo King 3D was no different.

Unlike some other SIMs, this didn’t come with any compression straps to keep it rolled up. However, I didn’t find this a problem, as it stayed together well once the air valves were closed, and I placed it back into its stuff sack.


I’ve only used this once so far on a cold winter camp, and so far I’ve been very impressed with this Thermarest SIM.

It gets the Thumbs Up from us.


So we’ve been using the Thermarest MondoKing 3D now for the past year. I really like this SIM.

It’s comfortable. It’s warm. And it’s reliable.

The only downside is that it is a bit harder to pack up than the new ‘smart’ valves on SIMs from Outwell and Vango. But that’s only a minor niggle.

It’s taken a lot of punishment over this last year, with both kids and dog in the tent. And it’s still going strong.

This SIM is an investment, but still recommended.

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Gav Grayston
Father to 3 kids, who loves getting out and about (hiking, running, camping, cycling, canoeing...) Co-founded Get Out With The Kids to help other parents enjoy the outdoors with their family.
Gav Grayston


Family adventures, activities, camping, holidays, OS #GetOutSide champions 2017 & 2018 #DofE brand ambassador @Craghoppers Partnership @campandcarvan @_elddis_
Gav Grayston
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