as the sleeping surface of the mattress 12 see fig2 4 and a peripheral skirt portion 22 attached thereto to form box like corners the peripheral skirt portion 22 has a sufficient depth which exceeds the depth of the mattress to allow excess material for forming a peripheral underhang portion 24 although fig1 does not show the mattress 12 the orientation of the parts of the bottom skirt member are oriented as though affixed to the mattress that is the peripheral skirt portion 22 depends from the main portion 21 at about a right angle with the underhang portion encircling a short distance beneath the mattress in the plane of the lower surface of the mattress for comfort purposes a pad 26 is sewn to the undersurface of the main portion 21 of the sheet member 20 referring also to fig3 for affixation to the mattress 12 the terminal end of the underhang 24 is provided with an open hem portion 27 through which is threaded a pair of elastic members 28 each being of a length sufficient to encompass one half the perimeter of the underhang 24 the free ends 28a of the elastic members 28 are passed through slide lock members 29 to form a drawstring at diagonally opposite corners for enabling adjustment of the tension of the elastic members 28 with the sheet member 20 fitted to the mattress 12 this arrangement provides full encirclement of the underside of the mattress by both the underhang and the elastic members 28 thus providing a sturdy fitting bottom.