Some campgrounds you can only reach on foot. On a trip like that, everything you sleep on has to be carried in, so the thick mattress from the rooftop tent stays at home.
Featured inBest Camping Mattresses of 2026
I took the Sea to Summit Camp Mat SI on a camping trip to a walk-in campground. It’s a self-inflating mat that weighs 780 g in Regular and rolls into its own stuff sack, and with an R-value of 4.2 it keeps the cold of the ground away from you.
What You’re Getting
A self-inflating sleeping mat from Sea to Summit with foam insulation, a multi-function valve and a Pillow Lock system, in a stuff sack. We tested the Regular size: 51 × 183 cm, 3.8 cm thick, R-value 4.2.
The good
- Very easy to set up with a few big breaths
- R-value of 4.2 for cold ground
- 780 g in Regular
- Multi-function valve for inflating, fine-tuning and fast deflating
- Pillow Lock patches keep a pillow in place
- Easy to roll up again
The not-so-good
- Comfortable enough, but not super thick at 3.8 cm
- Regular size is 51 cm wide
Quick Specs
| Spec | Details |
|---|---|
| Brand | Sea to Summit |
| Model | Camp Mat SI (self-inflating)Regular |
| Weight | 780 g821 g on our scale in its stuff sack |
| Dimensions | 51 × 183 cm |
| Thickness | 3.8 cm |
| R-value | 4.2 (ASTM F3340-18) |
| Mat fabric | Polyester with TPU lamination |
| Insulation | Polyurethane foam |
| Valve | Multi-function: inflateFine-tuneFast deflate |
| Other sizes | LargeRegular Wide rectangularLarge rectangular |
| Extras | Pillow Lock patchesStuff sack |
Setting it up
Out of the stuff sack, the mat is a tight green roll. Unroll it, open the valve, and it starts to fill by itself as the foam inside expands. It’s very easy to set up. The foam does part of the work, and a few big breaths finish the job. After a walk in with a pack on, that’s a lot nicer than blowing up an air pad from empty.
The valve has more than one job. In the inflate setting it’s one-way, so air goes in and doesn’t come back out between breaths. Press the centre and you let a little out to fine-tune how firm the mat is. Open the whole valve and the air rushes out. Rolling up is easy too: with the valve open, the air goes out as you roll, and the mat slides back into its stuff sack without a fight.
Comfort and warmth
The mat is 3.8 cm thick. It’s comfortable enough, but it’s not super thick, and that’s the trade-off for the light weight. If you’re used to an 8 to 10 cm mattress in the car or the rooftop tent, you’ll notice the difference. What you get in return is a mat you can carry: the foam inside supports you across the whole mat, and it doesn’t bounce or wobble the way a tall air pad can.
The foam is also what makes it warm. The R-value of 4.2 means it insulates well from cold ground, more than many air pads that are twice as thick. If you want to know what that number means for your trips, see our guide to R-values.
Pillow Lock
In the bag with the mat are four stick-on patches and an instruction sheet. You stick the patches to the head end of the mat, inside the marked outlines, and they grip the base of a Sea to Summit pillow so it stays where you put it. We combined the mat with the Sea to Summit Aeros Premium Pillow, the blue one in the photo. If you want to see the system in detail, we’ve written up how the Pillow Lock works.
It’s a small thing, but a pillow that slides off the mat at 2 am is one of the more annoying parts of sleeping in a tent, and this fixes it.
Size & Weight
The Regular is 51 × 183 cm, a tapered shape that’s wider at the shoulders. It’s listed at 780 g, and ours weighed 821 g on the scale in its stuff sack. For a foam-filled mat that’s light: the other self-inflating mattresses we’ve tested weigh more than 3 kg.
If you’re taller or like more room, the mat also comes in Large and in two rectangular versions.
Conclusion: Sea to Summit Camp Mat SI
The Camp Mat SI is a simple, warm sleeping mat. It inflates itself, the valve makes fine-tuning and packing up easy, the R-value of 4.2 handles cold ground, and at 780 g it’s light for a foam mat. It’s comfortable enough but not super thick, which is the trade-off for the light weight. I paid $140 for it. For ultralight hikers who want a mat that inflates itself, it’s a very good choice.
For the other mats we’ve tested, see our best camping mattresses guide.
A 780 g self-inflating mat with an R-value of 4.2 that’s very easy to set up and roll up again.
It’s comfortable enough but not super thick at 3.8 cm, and the Regular is 51 cm wide. It’s a very good choice for ultralight hikers.
- Ultralight
- Hikers
Yes. I paid $140, and for that you get a 780 g mat that’s very easy to set up and pack away, with an R-value of 4.2. If comfort matters more to you than weight, a thicker mat is the better buy.
