Spotlight - equipment views and reviews from the AK team
How do self inflating sleeping mats work?
21, Apr, 2010
Ever thought of your sleeping mat as a cheese toastie? Jim explains the similarities, as well as how your self-inflating sleeping mat works
The perfect choice for any camper is a bed that is comfortable, packs down to the size of matchbox and is warm to sleep on. An airbed is heavy and takes an age to inflate. A balloon bed packs down small but like an airbed can be cold because there is nothing to stop the air circulating around the inflated chambers. Whilst closed cell foam mats are light, can't be punctured and prevent heat loss into the ground, they don't offer a great deal of comfort. Self-inflating mats aim to combine the best properties of all without the need to carry a foot pump.
Self-Inflating Mats - the concept
A self-inflating mat is basically a layer of compressible foam sandwiched inside an airtight envelope of fabric with a sealable valve. When you open the valve the foam expands, sucks air into the mat and after a couple of minutes the mat will be semi-firm. You'll then need to add a few breaths of air to make the mat firm enough to sleep on. The foam provides the insulation and a built in pump, the sealed fabric in combination with the foam provides comfort and the whole mat squeezed flat for compact storage. Life would be simple if it was a one mat world but like all things compromises have to be made.
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 first self inflating mats, the inventors Jim Lea and Neil Anderson used a highly modified sandwich maker to make their first prototypes. However you can't just stick fabric together, you need a glue. In our original range of Airic sleeping mats we used a thin membrane of TPU plastic that was laminated to the inner surface of the fabric. This TPU membrane can be melted together to create an airtight layer. The TPU laminate is the first choice for many of the high end manufacturers but without careful monitoring and inspection potential hidden de-lamination defects can occur. Our OEM partner for self inflating mats developed and patented an alternative method to the TPU laminate using a PU coating. His factory still continues to refine this process and all the fabric is coated in-house ensuring their high quality standards are maintained at all times. Many cheaper brands of mat use a PVC coating as the "glue" which is much cheaper but is a well know environmental baddie as it can contain toxic additives.
Our mats use a variety of different fabrics depending on their expected use.
33D Ripstop Nylon
Extremely hardwearing for its weight we use this on our Airo mats. Show this fabric the respect it deserves and it will reward you with many good nights sleep.
A bombproof hardwearing fabric that doesn't need so much love and care as the lighter 33D. We use this on our Dirtbag and Wideboy mats to ensure you stay comfortable wherever your adventures may take you.
Polyester is the workhorse fabric in our range. We use it on the Dozer, Base and Little Kippa 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 its manufacture to give it a softer feel than typical synthetic fabrics. We use this on the Dozer to make sure it feels just like you're sleeping in your bed at home.
In the heart of every self inflating mat is a layer of open cell foam. We use open cell foam because it can be compressed easily for pack size but it recovers back to its original shape to help the mat self inflate. The reason open cell foam can do this is because all the tiny chambers within the structure of the foam are connected. Whilst it is possible to force air into or out of these tiny chambers it is very hard for air to circulate naturally when sealed providing a good thermal membrane. The open cell foam inside every sleeping mat has been specified to be the perfect balance between weight, inflation time and durability.
Die cutting a foam core can reduce the overall weight of a mat by up to 30%. This has the negative effect of reducing the insulation properties of the mat as it creates larger chambers that can circulate air. We use different die-cut profiles in our mat range to balance weight reduction with insulation.
This removes the maximum amount of foam whilst retaining enough material to allow the mat to self inflate and provide adequate insulation.
The circular pattern lightens the foam weight by around 20%. Used in our thicker pads there is enough foam retained to help provide support when using the mat partially inflated.
Selective Die Cut
Where 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.
The foam core of a self-inflating sleeping mat has tiny circular cores of foam removed along their entire length and sometimes their width to create air inflation tubes. This helps the foam recover and inflate the mattress to its full thickness faster.
The valve on a mat seals the air inside making it hard enough to sleep on without touching the ground beneath. Our Dozer has two valves to help inflate and deflate quicker. The shape of the valve makes it easy to continue blowing into the valve as you twist it to seal, ensuring you can achieve the desired hardness.
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 compression straps run around it to help close it up tight. A hidden pocket inside the bottom of the bag stores a repair kit should the worst happen when you're away.
NumoThick big chamber 2 - 3 season full length sleeping mat weighing just 350 g, packs down smaller than a self-inflating mat saving space in your sack£44.99
Airo 120Torso length self-inflating mat, weighing 450 g it is lightweight, durable and extremely packable Airo 120 is loved by lightweight adventure seekers£34.99
DirtbagThe fattest baddest self-inflating mat for all those dirtbag moments in your life, weighing just 900 g it is comfort you can carry£54.99