fig1 illustrates a conventional mattress set being used with the present invention . a lower mattress 10 generally comprises some form of box springs , while an upper mattress 12 is usually referred to as simply &# 34 ; mattress .&# 34 ; use of the term mattress hereinafter is intended to refer to an upper mattress unit such as 12 . mattress 12 and box springs unit 10 usually are manufactured or selected so as to be used in paired units . conventional sizes of mattress 12 and springs 10 are known by the terms standard ( or twin ), full , queen and king . the mattress pad 14 of this invention may be of any size in relation to a given mattress 12 , but typically has the same rectangular dimensions as the conventional size mattress with which it is intended to be used . for larger - sized conventional mattress , such as king - sized mattresses , mattress pad 14 may be split into two or more units , as further illustrated and discussed in fig2 below , for convenience in packaging , shipping and / or manufacturing . referring again to fig1 a mattress pad 14 is illustrated in place on top of a mattress 12 , which in turn rests on box springs 10 . sheet 16 which is placed on top of mattress pad 14 illustrates a conventional sheet , in this instance a fitted sheet , which may be ordinarily applied to mattress 12 . in fig1 sheet 16 is mostly in place over both mattress 12 and mattress pad 14 , but is partially pulled back to more clearly illustrate the relationship of mattress pad 14 with its supporting mattress 12 . of course , sheet 16 may also alternatively be a conventional flat sheet , as discussed above . a plurality of projections 18 are formed on mattress pad 14 , as well as flat marginal regions 20 and 22 along certain edge portions thereof . these features are more clearly illustrated in the cross - section of fig2 and 3b . the mattress pad 14 may itself be comprised of various resilient materials , but in the preferred embodiment comprises 100 % virgin polyurethane foam to provide a consistent quality of touch and feel to the user . various densities of material may be used , but a density of approximately 1 . 6 pounds per cubic foot is preferred . likewise , all materials which are functionally equivalent to polyurethane foam are included within the scope of this invention . an overall thickness of approximately two inches is also preferred , but a range of thicknesses may be suitable for practice of the invention . referring to fig2 a cross - section of fig1 as indicated therein is illustrated . mattress pad 14 rests atop conventional mattress 12 . since the rectangular dimensions of mattress pad 14 are specifically in accordance with the associated mattress 12 in this instance , the width of pad 14 is shown as the same as mattress 12 . a plurality of projections 18 are illustrated as basically sinusoidal curves formed regularly in a pattern on an upper side of mattress pad 14 . side 24 of mattress pad 14 which rests on the upper surface of mattress 12 is a relatively smooth surface . thickness &# 34 ; b &# 34 ; illustrated in fig2 represents the distance between the smooth surface 24 and an imaginary surface parallel thereto defined by the peaks of projections 18 . this thickness is approximately two inches , as discussed above . as further illustrated in fig2 planar ledge or marginal region 20 ( on the left hand side of fig2 ) and planar ledge or marginal region 22 ( on the right hand side of fig2 ) are generally flat surfaces , devoid of any projections . the precise width of such regions ( eg ., the distance between points 26 and 28 of fig2 ) is preferably about one inch , but may be varied in accordance with this invention . the surface defined by the surfaces of either of marginal regions 20 and 22 may be described as a margin surface which is parallel to the imaginary surface defined by the peaks of projections 18 , and also parallel with the flat surface 24 which forms the bottom of mattress pad 14 . width &# 34 ; a &# 34 ; of fig2 illustrates the distance between such a margin surface and the flat bottom surface 24 of fig2 . width &# 34 ; a &# 34 ; is preferably about one inch , but is usually about one half of width &# 34 ; b &# 34 ; , whatever width &# 34 ; b &# 34 ; is selected to be in a given embodiment of the present invention . dotted line 30 of fig2 illustrates one possible dividing line of mattress pad 14 , as discussed above . for example , if mattress 12 is a king - sized mattress , for convenience in both manufacturing and marketing , mattress 14 may actually comprise two sections intended for edge - to - edge placement during use , as indicated by dotted line 30 . fig3 illustrates another cross - section of fig1 along the indicated plane thereof which differs from the fig2 cross - section . conventional mattress 12 is covered first with a mattress pad 14 in accordance with this invention , and then with a conventional sheet , such as fitted sheet 16 . fitted sheet 16 has elastic members 32 for a secure fit around mattress 12 . the plurality of projections 18 typically are only slightly depressed by the addition of sheet 16 . in contrast , marginal regions 20 and 22 resiliently receive the portions of sheet 16 which wrap around the uppermost edges of mattress 12 . in doing so , marginal regions 20 and 22 flex to form an angled surface generally downward from points 26 and 27 , respectively , so as to accommodate sheet 16 in a manner which lessens the upward force thereon by projections 18 at the farmost edges of mattress pad 14 . by resiliently receiving sheet 16 in such a fashion , the thickness &# 34 ; b &# 34 ; of mattress pad 14 may be maximized for increased user comfort , while minimizing the upward thrust effect on sheet 16 at those particular portions thereof which would cause elastic members 32 to be drawn off of the bottom edge of mattress 12 . fig3 a illustrates an enlarged view of the left hand section of a conventional mattress 12 in use with a typical prior art mattress pad 40 . for purposes of direct contrast with the present invention , prior art mattress pad 40 is illustrated as having a plurality of projections 42 which are similar to projections 18 of the present invention . likewise , conventional sheet 16 is also applied to mattress pad 40 and mattress 12 , as in fig3 . in contrast however , prior art mattress pad 40 does not have any flat marginal regions 20 and 22 ( i . e ., &# 34 ; flat &# 34 ; whenever no sheet is applied ) as illustrated in fig2 . consequently , the upward force f applied in fig3 a near the uppermost left hand corner 44 of mattress 12 is much greater due to projection 46 than the upward force f &# 39 ; of fig3 b on sheet 16 at the analogous portion of the present invention . this greater force f of the prior art tends to push upward on sheet 16 to a degree sufficient to cause elastic member 32 of sheet 16 to be pulled from around the lower edge 48 of mattress 12 . whenever such a pull - off event occurs , sheet 16 may be less snug across mattress 12 and mattress pad 40 , and thereby provide physical and psychological discomfiture to the user , which virtually defeats the purpose of a supplemental mattress pad . in contrast , as illustrated in fig3 b of this application , the present invention provides a mattress pad 14 having at least one marginal region , such as marginal region 20 , which resiliently receives a conventional sheet 16 onto a conventional mattress 12 so that elastic member 32 of sheet 16 is not pulled from around edge 48 of mattress 12 . a much smaller upward force f &# 39 ; at corner 44 of mattress 12 is illustrated than the upward force f of prior art fig3 a . the smaller force results from the compression function of the marginal region 20 in response to the presence of sheet 16 . furthermore , the projection ( or row of projections ) 50 which are closest to marginal region 20 remain relatively unaffected by the presence of sheet 16 . by contrast to the prior art , with reference to fig3 a , if sheet 16 were pulled sufficiently tight for elastic member 32 thereof to gather around corner 48 of mattress 12 , the projection 46 of mattress pad 40 would be detrimentally forced inward instead of undisturbed , as with the present invention . moreover , the force f would generally increase the more that projection 46 was pushed down by sheet 16 . fig3 b illustrates further projections 52 in dotted line . these dotted line projections are intended to represent an alternative arrangement of the projections 18 on the upper surface of pad 14 , wherein alternating rows of sinusoidal surface projections 18 are staggered so that the peaks of one row of projections ( such as 18 ) are matched with the hills of an adjacent row of projections ( such as projections 52 ). as a further alternative , though not shown , shapes other than sinusoidal may be used . these may include pyramid shapes , square or rectangular shapes , circular shapes , or any other geometrical or nongeometrical shapes , all of which may be truncated or not . such modifications to the illustrated figures and any other modifications which would occur to one of ordinary skill in the art are intended to be included within the scope of the present invention . variations of embodiments based on selections and mixtures of the various different features illustrated and disclosed also form part of this invention . furthermore , all such modifications and variations are also intended to be included within the meaning of the following claims , which further define and describe this invention .