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Self-inflating mats for bedtime comfort

As campers we soon learn that a sleeping bag is only as good as what you place underneath to protect against the cold hard ground.

In fact, the old camping practice saw one third insulation above and two thirds beneath for a good night’s sleep – your sleeping bag providing the upper insulation and a mattress or mat providing the bottom insulation. Today’s camper is lucky to benefit from self-inflating mat technology that uses the latest manufacturing techniques and modern materials to bring home comfort to the pitch.

The self-inflating mat (or SIM) overcomes many of the problems experienced by other forms of mattress. For instance, the air bed may provide a comfortable base on which to rest but the internal mass of air can sap body heat unless you add extra thermal insulation between you and the ground. This is often a blanket or the simplest mattress − a sheet of closed-cell foam that traps insulating bubbles of air between the airbed and the ground. Of course, such a foam mat can also be used on its own but, while they conserve body heat, they do not offer the best padding from stones and bumps in the ground. 


A SIM comprises of an ‘airbed’ style outer filled with open cell foam that starts to expand and draw in air to self-inflate as soon as you open the valve. Once the mat is fully inflated you blow in a little more air to adjust firmness to suit personal taste before closing the valve. If the mat is too firm, just let out a little air. The aim is to have something that supports rather than feel like a paving slab.
The foam has a ‘memory’ and this is effected if compressed for any length of time. When you first use a SIM or use it after being stored for long periods in its deflated state, you might have to blow in air to help it regain its shape. It is worth minimising the amount of air you blow into a mat – the moisture introduced can cause the growth of mould that can adversely affect the foam. Some SIM valves will accept a pump to get around this.

This neatly leads us on to storage and use. It is good practice to store a SIM in its inflated state with the valve open. This ensures the foam maintains its memory and any moisture trapped inside evaporates away. Many campers store SIMs behind furniture, like wardrobes. 
When in use, it is also good practice to open the valve during the day. Not only does this help any moisture to evaporate away but any changes in air pressure due to daily temperature fluctuations will not damage the SIM.

SIMs can be purchased in various shapes, sizes and thicknesses to offer numerous insulation and comfort levels. Most campers use a rectangular mat to maximise the sleep surface. However, SIMs with a tapered ‘mummy’ profile save weight and reduce packed size by losing excess material. Smaller SIMs can be purchased for children and here you can get away with a thinner mat for there is less body weight to compress the insulation.

If storage and transportation space is at a premium, remember that, while so comfortable, the weight and bulk of a SIM increase the thicker it gets. And the thicker it gets the harder it is to pack away. As soon as you open the valve to roll up your SIM you start to fight against the foam’s ability to suck in air. This makes life very difficult unless…

First, open the valve. Next, fold the mat into thirds towards the valve, pressing your body weight down to remove air each time you fold it over. Close the valve to prevent air from being drawn in.
Unfold the mat and start to roll towards the valve. Open the valve once you meet air resistance and continue to roll up the SIM to remove excess air. Close the valve.

If there is still too much air left in the SIM, unroll and tightly roll up again until you meet air resistance. Open the valve and continue to roll until all air is expelled. This will be far easier…
SIM maintenance is simple. Clean, dry and store, where possible, unrolled with the valve open. Any punctures can be treated like a bicycle tyre.

Outwell offers a choice of market-leading single and double SIMs in different thicknesses to suit needs. Outwell SIMs include award-winning innovations that add to versatility, performance and ease of use. And there are plenty of options to make our SIMs even more comfortable, including stretch sheets and pillows.