If you look at photographs of the British Army on manoeuvres in the field from the 1980s onwards, you can often see a large foam cylinder strapped to the side of their bergans:This cylinder is a foam sleeping mat, a thin ¼ inch piece of foam that can be rolled out to provide a rudimentary lightweight mattress in the field, it is rolled to leave the dark green side outermost:Brass eyelets are fitted to one edge to allow elastic cords to be attached to hold the rolled mat closed:The interior of this particular mat is white, presumably to allow the mat to be used in arctic conditions as well as temperate ones:‘18GN05’ is stencilled on the end in yellow:These mats are widely decried as being pretty useless and far too thin to offer any real comfort, however they do provide a waterproof layer between the sleeper and the ground and help reduce the loss of body heat into the floor. Many troops have started replacing these sleeping mats with self inflating examples, however some prefer the old style foam roll mat:
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.
I have used one of these mats myself before now, sleeping in a wooded area under a bivvi- the sleeping mat did very little to stop my back being poked all night by tree roots! These mats are naturally shiny, so many troops get fabric covers made that can be placed over teh mat and reduce the reflection when on the march.