Sleeping in the field has never been an entirely comfortable affair, and whilst it is true that most soldiers can sleep on a washing line, some form of insulation between the body and the ground does help ensure that body heat is not lost and a more restful sleep can be achieved. The need for some sort of padding and insulation first began to be recognised in the 1980s and a roll of foam was issued to act as a sleeping mat. This was thin and offered limited insulation, but was still relatively bulky when rolled up. By the 21^st century technology had improved and the British Army adopted an inflatable roll mat, based on designs developed for civilian camping gear. This was a self-inflating mat that could be folded in half lengthways before rolling up to make a more compact bundle that fits better into a bergan. Here, unpacked, the full size of the sleeping mat can be seen:

It is not full length, but offers comfort and insulation to the body’s core where heat retention is most important. The mat has a valve at one end:

Unscrewing the valve allows air to enter the mat and slowly inflate it, foam cells inside pushing up and allowing it to self-inflate without the need to physically blow it up. Conversely by opening the valve and rolling the mat back up the air is forced out creating a more compact package. Once rolled up, it can be placed inside a protective bag, with a couple of loops of elastic to help hold everything tight:

A label is sewn to the storage bag with space for a soldier’s name and number to be written on:

A set of instructions are printed on a large label sewn to the mat itself:

The short length of this design has not made it universally popular amongst soldiers:

I was issued a blow up self inflating type roll mat, used it once and reverted back to the foam type. quicker, easier, no valve to fall out and the issued foam type cover the whole body. blow up ones only the head and torso, giving me bloody cold legs. Flippin devils work. 

Others however were more favourable about the design:

Takes up less space than a full-length roll-mat, and doesn’t soak-up water, (unlike a roll-mat). Plus, with a little effort…you can double its effective thickness.

The increase in thickness the writer is alluding to here is to physically blow air into the mat with your mouth to give it extra thickness and insulation.