How Do Self-Inflating Sleeping Mats Work?

By Alpkit

The perfect choice for any camper is a bed that is super comfortable, packs down to the size of matchbox and is warm to sleep on. The matchbox-sized sleeping mat is still in development but we think we've found a solution in the meantime!

Closed cell foam mats are light, insulating and can't be punctured but they aren't very comfortable. Inflatable mats are comfy and pack down small but can be cold because there is usually nothing to stop the air circulating around the inflated chambers.  Self-inflating mats use compressible foam insulation and inflate like an airbed, combining the best properties of both.

  1. How do self-inflating sleeping mats work?
  2. Alpkit's sleeping mat construction
  3. What fabrics we use
  4. What is die cut open cell foam?

Blowing into a self-inflating sleeping mat at a campsite to top up the air

How Do Self-Inflating Sleeping Mats Work?

A self-inflating mat is basically a layer of compressible (open cell) foam sandwiched inside an airtight envelope of fabric with a sealable valve. When you open the valve, the foam expands and sucks air into the mat. After a couple of minutes the mat will be semi-firm but you may need to add a couple of breaths of air to make the mat firm enough to sleep on.

The foam works as a built-in pump and provides the insulation by trapping still air within the mat. The sealed fabric, in combination with the foam, provides a comfortable springy platform to sleep on. And, because the foam is compressible, the whole mat can be rolled away into a compact package by squeezing all the air out.

Life would be simple if it was a one-mat-world (one mat to rule them all one mat to find them...). However, as with all outdoor gear, sometimes compromises have to be made when prioritising warmth, weight, pack-size or comfort.


A diagram of how self-inflating sleeping mats work by prevented air circulation and heat loss by convection
A Dirtbag self-inflating sleeping mat fully inflated

Construction

To understand how a self-inflating mat is made, think about how you would make a cheese toastie... only the bread is replaced by fabric and the cheese replaced by foam! In fact, during the early development of Thermarest® (the very first self inflating mats), inventors Jim Lea and Neil Anderson used a highly modified sandwich maker to make their first prototypes!

But you can't just stick fabric together: you need a glue. In our very first sleeping mats (the Airic for the AlpHistory buffs), we used a thin membrane of TPU plastic that was laminated to the inner surface of the fabric, creating an airtight layer. Most high-end brands use this construction but, without careful monitoring, defects in the lamination can occur. We now use a patented PU coating instead which is more reliable and easier to ensure a high level of quality control. Cheaper mats may use a PVC coating as the "glue" to reduce costs but PVC is highly toxic and bad for the environment.

An Airo 180 self-inflating sleeping mat held side on to show the construction

Fabrics

Our mats use a variety of different fabrics depending on their expected use.

40D Diamond Ripstop Nylon – Extremely hardwearing for its weight, we use this on our Airo 120 and Airo 180 mats. Treat your Airo with a bit of love and it will reward you with a good nights sleep, trip after trip.

50D Nylon – A bombproof hardwearing fabric that doesn't quite as much care as the lighter 40D. We use this on our Dirtbag mats to make them extra hardwearing without adding loads of unecessary weight.

75D Polyester – Polyester is the workhorse fabric in our range. We use it on the Dozer and Double Dozer because it offers great value for money whilst providing the durability required by a sleeping mat.

75D Peach Polyester – The surface of this fabric has been brushed during manufacturing to give it a softer feel than typical synthetic fabrics. We use this on the top of the Dozer and Double Dozer to make sure they feel just like your bed at home. (Well, you might not think so if you sleep in high thread count Egyptian cotton!)

Sleeping on an Airo 180 self-inflating sleeping mat in a tent

Foam

Inside every self-inflating mat is a layer of open cell foam. We use open cell foam because it can be compressed easily for a smaller pack size, whilst still offering loads of insulation. It also recovers back to its original shape easily, helping the mat to self-inflate.

Open cell foam is so compressible because all the little air chambers inside the foam are interconnected, unlike the closed cell foam we use for traditional roll mats. Although air can pass in and out of the foam, it's very hard for air to circulate inside the mat when you're sleeping on it. Still air is highly insulating and it means you don't lose heat via convection like you can with inflatable sleeping mats.

What Does Die-Cut Foam Mean

Open cell foam pads can be cut in lots of different ways to produce the perfect balance of weight, inflation time and durability. A process called 'die cutting' can reduce the overall weight of a mat by up to 30%.

The downside of this is that it reduces the mat's level of insulation, creating larger chambers that allow air to circulate. We use different die-cut profiles in our mat range to balance weight reduction with insulation:

Matrix – This diamond-shaped pattern removes the maximum amount of foam whilst retaining enough material to allow the mat to self inflate and provide adequate insulation.

Dot Matrix – The circular pattern lightens the foam weight by around 20%. We use this in our thicker pads as there is enough foam retained to help provide support when using the mat partially inflated.

Selective Die Cut – When insulation and support are crucial to retain the mat's comfort, we only die cut the foam in low load areas, such as the feet.

Foam Coring – The foam core of a self-inflating sleeping mat has tiny circular cores of foam removed along the entire length (and sometimes the width) to create air inflation tubes. This helps the foam recover and inflate the mattress to its full thickness faster.

A valve for a self-inflating sleeping mat, allowing air in

Valve

The valve on a mat seals the air inside making it hard enough to sleep on without touching the ground beneath. Our Double Dozer has two valves to help it inflate and deflate quicker. The shapes of our valves makes it easy to continue blowing into the valve as you twist it to seal, ensuring that you can achieve the desired level firmness.

Stuff Bag

All our sleeping mats come with a storage sack as standard. The bag is tapered making it easy to slide the rolled mat inside and we include elastic compression straps so it doesn't unroll on you before you can get it in!. All Alpkit sleeping mats come with a puncture repair kit should the worst happen while you're away... accidents happen! And pointy rocks do stick into backs...

1 comment

  • Can you send me inflation instructions for the dozer as it has three valve positions- which one is needed or best for inflation?

    Shaun

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