thick intermediate layer 6 will be between 3 16 and u215d inch thick and bottom layer 7 will be approximately u215b inch thick furthermore belt 10 will have a substantially greater width than thickness as shown in fig1 and will have a generally rectangular cross sectional configuration intermediate layer 6 has longitudinal strengthening cords 11 extending lengthwise throughout cords 11 are disposed internally of belt 10 in longitudinal spaced apart parallel relation cords 11 provide increased strength to belt 10 for its tensioning without undue elongation or stretching and to assist in retaining it 39 s rectangular relatively smooth shape only a portion of the total number of cords 11 are shown in cross section in fig2 as shown in fig1 and 2 belt 10 may have two similarly shaped arrays 12 and 13 of single or multiple grooves 17 in its lower layer 7 areas or arrays 12 13 are preferably spaced equidistant from the edges 29 of the belt 10 and generally one quarter of the width of belt 10 to provide fold over or flap portions 14 15 which extend from the central medial portion 16 of belt 10 grooved areas or arrays 12 13 preferably have the same number of similarly shaped grooves 17 to obtain comparable fold over effects when end flaps 14 15 are rotated through an angle of about 180 u00b0 or less end flaps 14 15 are capable of swingable folding movement over medial portion 16 after a load is disposed on the central belt portion 33 as shown in fig2 grooved array 12 is shown having four similarly shaped grooves 17 that provide a unitary fold line.