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Therm-a-Rest MondoKing 3D XXL Sleeping Pad Review

Therm-a-Rest know sleeping pads. They’ve been making them for 50 years. But can they make a 5 pound, 4 inch monster than could replace your mattress at home? We tested the MondoKing 3D XXL to find out.

What is the MondoKing 3D Sleeping Pad?

The MondoKing 3D is a bit different than most other Therm-a-Rest sleeping pads. It’s huge. It’s 4.25 inches thick. It’s 30″ wide by 80″. Clearly a big, thick car camping mattress.

Two TwinLock one-way valves fill up and dump air. The stuff sack doubles as a pump sack and hooks onto the ‘in’ valve, letting you inflate with dry air.

Inside StrataCore construction is basically lightweight foam with horizontal sections cut out. These give MondoKing it’s ridged look and allowed it to be rolled up easily and quickly.

We spent a bunch of nights on the mattress to test it’s comfort and packability. Let’s see how it did.

Best Camping Mattresses of 2023

The MondoKing 3D XXL was part of our Best Camping Mattresses of 2023 test. See the rest of the mattresses here:


  • Very comfortable
  • Easy to roll
  • Fast to self-inflate


  • Can’t easily let a bit of air out
  • Sides slope down slightly


  • StrataCore construction
  • 4.25″ (11cm) thick
  • 7 R-value
  • Twinlock Valves
  • Vertical sidewalls
  • $274.95 USD ($384.98 CAD)
  • 5 pounds 8 oz (2.5 kg)
  • 30″ x 80″ (76 x 203cm)
  • 31″ x 10.3″ packed (79 x 26cm)
  • 50d polyester knot top
  • 75d polyester bottom


Inflating the MondoKing is pretty quick. Opening the one-way in valves lets in air quickly and it was maybe a minute to self inflate. From there I inflated with the pump sack or blowing it up.

The ‘in’ valve sticks out a bit from the mattress like other Therm-A-Rest classic valves except it’s just one way, you can stop putting air in and it stays in the mat.

It took about 1 minute to blow up the rest of the mat from self-inflated, or 2 minutes from self inflated with the pump sack. There’s certainly a trick to the pump sacks that takes getting used to and I’m not great at it so you could probably get it faster. The pump sack snapped onto the valve well and stayed there the whole time I was adding air.

I wasn’t able to inflate this one with a pump because of how the valve sticks out from the mat. I didn’t have a connection from my little pump that fits it.

Self-inflate1 minute
Inflate from self-inflated – Blowing up1 minute
Inflate from self-inflated – Pump sack2 minutes
Inflate from self-inflated – Pumpn/a
Inflate from nothing – Pumpn/a
Inflation times for the MondoKing


Sleeping on the MondoKing is great. It’s very soft and comfortable.

I thought sleeping on the the horizontal ridges on top would feel strange but I barely felt them laying them. They compress easily when you lay on them.

I tent to sleep on my side and as with all the mattresses tested, having a taller pillow setup than at home worked better. The air mattresses don’t compress quiet like a mattress at home does.

The 4.25 inches of foam easily kept me off the ground, even sleeping on my side. I had to take a lot of air out for me to be on the ground and it wasn’t comfortable with that little air anyways.

There are 2 things that aren’t bad about the comfort but are something to note.

The horizontal ridges across the top slope down slightly near the edges, so while the top is basically flat, it feels like there’s a slight slope down. The sides of the mat are still vertical but it feels slightly narrower because of the slope. There’s still plenty of room with the 30″ width.

The second thing is adjusting the amount of air in the mattress.

The ‘out’ valve is good and doesn’t let any air out but there’s no way to let a tiny bit of air out at a time without opening the valve a lot. If you’re laying on the mattress, the air comes out quickly. One-way ‘in’ valves that can be pushed in slightly to let the air out let you adjust the air a little better.

Deflating and Packing

Deflating is easy with the ‘out’ valve’. Simply unscrew and it dumps air quickly and it’s one-way so the air stays out while you’re wrestling with it trying to pack it all up.

There’s only one ‘out’ valve so it’s a hair slower to dump air than mattresses with 2. I could deflate ,roll, and pack the MondoKing into it’s bag in less than 2 minutes so it’s not a big issue.

With the horizontally cut StrataCore foam inside, it’s very easy to roll up. Some mats want to sprint open and smack you in the face while they do it, but not the MondoKing. The trimmed out foam makes it easier to roll. And the one-way valve keeps the air out.

The stuff sack takes a bit of fiddling to get around the mat but it’s not terrible. The stuff sack is properly sized for a bit of extra room when the mat is rolled well. I do prefer mats with straps and side access bags though as they’re less of a wrestling match to pack up.


At 5 pounds 8 oz (2.5 kg), the MondoKing is on the lighter end of the big mattresses we tested. Mattresses ranged from 3 pounds (just air, no foam) up to almost 8 pounds.

Unless you’re counting grams, then weight on a mattresses like this won’t matter much. It fits in the truck or it doesn’t. The cooler and drinks will break your back carrying around, not the air mattress.


Air mattresses can be put into 2 categories, those that just roll up and those that can be folded and packed up smaller somehow.

The MondoKing is in the first category. It measures about 31″ x 10″ when packed up, basically just rolled.

Unrolled it’s 30 inches wide by 80 inches long. The extra length is nice for the taller folks (not me) and keeping your pillow and all limbs on the mat.

The slide slope to the edges felt like a little smaller than 30 inches wide but not enough to make a big difference.

The bottom of the 30″ x 80″ MondoKing

Who is Therm-A-Rest?

In 1971, a group of unemployed Boeing engineers were trying to make sleeping outside better. By 1972 they the Therm-a-Rest Standard 3/4, the world’s first self-inflating sleeping pad.

Since then they haven’t stopped making getting outdoors easier and more comfortable. Almost anyone who has slept outside has done so on a Therm-a-Rest at some point or another. They’ve reached the Kleenex status of product.

They not only make sleeping pads, but entire sleep systems and a whole range out high quality outdoor gear.

Therm-a-Rest operations under the Cascade Designs umbrella along with fellow outdoor companies MSR, Platypus, PackTown and SealLine.


The MondoKing 3D sleeping pad from Therm-a-Rest is an excellent sleeping pad that is easy to inflate and pack away.

The only 2 small improvements I would make would be having a strap with a sideloading bag, and a modified valve that could let small amounts of air out to tweak it while you’re on it. Both minor issues as once you get the air dialed the soft top and 4.25 inches of foam make a for a great night sleep.

Verdict: Recommended see our rating system

Usual Price: $274.95 USD ($384.98 CAD)

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