c and the inner surface of the side wall 12 a contacts and bears on the inner surface of the side wall 12 d the top flap 14 is then wrapped around the side wall 12 d in the direction indicated by the arrow in fig1 e through the configuration shown in fig1 f until the releasable engagement mechanism 14 a bears on and engages with a similar releasable engagement mechanism 12 g sewn on an outer surface of the wall 12 c so as to bring the container 10 to the fully collapsed configuration as shown in fig1 g it can of course be seen that by going through the steps in reverse the container 10 may be moved from the fully collapsed configuration back to the expanded configuration fig2 and 3 show respectively a longitudinal cross sectional view of the container 10 and a transverse sectional view of the container 10 taken along the line n u2014 n in fig2 as the structure of the side walls 12 a 12 b 12 c 12 d is the same only the structure of the side wall 12 a will be discussed below the side wall 12 a has an outer layer of an air permeable material 20 e g a synthetic material traded under the trade name 10d oxford nylon a middle layer of an air impermeable material 22 e g.