When I bought the folding officer’s camp bed we looked at a few weeks ago, it came with a portable, cork filled mattress, named to the same officer. These matresses were supplied to add an extra level of comfort to a camp bed and consisted of two pieces of green canvas (now long faded) that were stitched into long thin pockets, each filled with granulated cork:

These could then be rolled up into a handy size, secured with a strap and easily shipped with the rest of the officer’s baggage:

These mattresses were available from the Army and Navy stores amongst other places with a range of filling including hair and kapok for the cost of 36/- in 1939. I know though that this is a cork filled example as the fabric has become very fragile and there was a small tear in one of the panels when it arrived which spilt granulated cork as I unpacked it. This has now been repaired with a small patch, but the state of the canvas means I will not risk putting any weight on it.
The only markings I could find on the mattress are the officer’s name, inked onto the canvas in one corner:

The original colour of the mattress is clearly visible in the folds and it shows just how much the canvas has faded over the last eighty years.