referring now to fig1 , a hospital bed 10 or the like may provide for an articulating carriage 12 for supporting a mattress 14 thereupon . the articulating carriage 12 may provide , for example , multiple hinging sections 16 including a head section 16 a , center section 16 b , and foot section 16 c , that may be angled to flex the mattress 14 to conform with the sections 16 , for example , to raise the head of the mattress 14 or lower the foot of the mattress 14 . for this purpose , the mattress 14 may flex to follow motion of the sections 16 . referring now to fig2 , the mattress 14 , when unarticulated , may present a generally planar cushion having opposed broad surfaces presenting a soft face 18 a on one side and a firm face 18 b on an obverse side separated by a mattress thickness , for example , of five to eight inches . each of the faces 18 extends along the mattress length 20 from a head end 22 to a foot end 24 , for example , any of 76 , 80 , and 84 inches , and extends along the mattress width 26 between left and right sides , for example , of any of 35 , 39 and 42 inches . it will be appreciated that a variety of other dimensions may also be provided . the mattress 14 is generally sized to support a supine adult along its length ( the mattress length extending from head end 22 to foot end 24 ) on either of the soft face 18 a or firm face 18 b when that face is horizontal and uppermost . the soft face 18 a may be labeled with a firmness designator 30 such as the word “ soft ” or other similar phrase or symbol as well as manufacturer information 31 visible when the soft face 18 a is positioned on top . conversely the firm face 18 b may be labeled with a firmness designator 30 such as the word “ firm ” or other similar phrase or symbol together with manufacturer information 31 visible when the firm face 18 b is positioned on top . an indication of the head of the mattress 14 may be provided , for example , in the orientation of the firmness designators 30 being positioned to be read while facing the head of the mattress 14 or other designator ( not shown ). these firmness designators 30 may be applied directly to the outer faces of the elastomeric foam described below . referring now to fig3 , the mattress 14 may be constructed from multiple parallel laminated layers 32 and 34 each of an elastomeric foam material such as polyurethane foam . the foam layers 32 will generally have a width substantially equal to the width of the mattress 14 and a thickness being a fraction of the thickness of the mattress 14 so that the number of layers 32 times their thickness equals the thickness of the mattress 14 . the width may be reduced slightly when side bolsters 76 are used as described below . all but the outermost , softest of foam layers 32 a will have a length slightly shorter than the length of the mattress 14 to extend from a head end 22 of the mattress 14 to a point just short of the foot end 24 of the mattress 14 where a patient &# 39 ; s heels would rest . this length will generally be at least three quarters of the length of the mattress . the outermost , softest foam layer 32 a may , in contrast , extend the full length of the mattress 14 . foam layer 34 will have a width generally equal to the width of the mattress 14 and a total thickness comparable to the thicknesses of the layers 32 minus the softest , outermost foam layer 32 a . the length of foam layer 34 will be such as to make up the difference between the length of the inner foam layers 32 and the length of the mattress 14 and so that layer 34 is positioned primarily beneath the heel of the patient when the patient is resting on the mattress 14 . in one embodiment , as shown in fig3 and 4 , layers 32 a - 32 d will be provided assembled together by adhesive into a unitary mattress core . specifically layer 32 a may be positioned proximate to the soft face 18 a and layer 32 d may be positioned proximate to the firm face 18 b . layer 32 a may then have its inner broad surface attached to a first broad surface of layer 32 b with the second broad surface of layer 32 b attached to a first broad surface of layer 32 c , and with the second broad surface of layer 32 c attached to the inner broad surface of layer 32 d . generally the layers 32 will each have a different firmness , for example , as designated by an indentation force deflection number ( ifd ), for example , as measured by astm d3574 for a uniform volume of material ( e . g ., a 15 ″ by 15 ″ by 4 ″ foam slab ). preferably , layer 32 a is softer ( lower ifd number ) than layer 32 d and layer 32 b will be softer than layer 32 c . layer 32 b , on the other hand , will be harder than layer 32 a , and layer 32 c will be harder than layer 32 d . accordingly , a relatively firm middle layer , for example including layers 32 b and 32 c , which is normally used on the bottom of medical mattresses , is placed in the center of the mattress 14 . positioning the firm layer in the middle of mattress 14 allows both top and bottom sides of the mattress 14 to provide improved weight capacity and pressure redistribution when used on either face 18 a or face 18 b . the layers 34 under the patient &# 39 ; s heel will desirably each provide low ifd values so as to reduce point pressures on the patient &# 39 ; s heel . this layer may be of uniform ifd value , for example , comparable to layer 32 a . layer 34 may be attached in a butt joint to the layers 32 by adhesive . one possible selection of foam values for each layer is provided in the following table : referring still to fig3 , the layers 32 and 34 when assembled may be covered by nomex ® or another fire resistant material 40 to provide a burn resistant “ sock ” which in turn may be covered by a stretchable fabric cover 42 possibly including waterproof qualities . this latter fabric cover 42 may provide for a zipper to allow it to be removed , cleaned , and then re - installed and includes the manufacturer information 31 and firmness designator 30 , described above , printed or embroidered on the outer surface . the cover 42 may , for example , be made of stafford cpu 150 fabric , commercially available from stafford textiles limited of toronto , canada , a stretchable fabric that reduces “ hammocking ” allowing better pressure redistribution . referring now to fig4 , in one embodiment , cover 42 at the portions extending over the sides of the mattress 14 may support hook and loop fastener strips 44 ( for example velcro ®) running generally horizontally along the vertically extending left and right edges and head and foot edges of the mattress 14 as stitched thereto . a bottom cover 46 having generally a central rectangular panel equal in area to the area of the soft face 18 a or firm face 18 b may have left and right extending flaps and headward and footward extending flaps 54 supporting mating hook and loop strips 55 . in this way , the bottom cover 46 may be attached to either cover the firm face 18 b when the soft face 18 a is facing upward to be used by the patient , or to cover the soft face 18 a when the farm face 18 b is facing upward to be used by the patient , as held in place by inter - engagement of the strips 55 and 44 . in either configuration of the bottom cover 46 , an outwardly exposed surface of the panel 50 may provide for patches of slip resistant material 56 such as a rubber that will frictionally engage the sections 16 of the bed 10 ( shown in fig1 ) to hold the mattress 14 in place during articulation of the bed 10 . referring now to fig5 , in an alternative embodiment , cover 42 may be attached to one vertical edge ( a right edge as shown ) of each of two rightwardly extending fabric strips 60 seamed at one edge to the cover 42 and having a length to be folded over or under the mattress 14 as indicated by arrows 62 . when so folded , the fabric strips 60 may releasably attach to an opposite edge of the cover 42 by means of hook and loop fasteners 64 on the strips 60 and corresponding hook and loop fasteners 66 on imposed vertical edges of the cover 42 . both sides of the strips 60 may be coated with a nonskid material 68 such as rubber or the like so that some nonskid material 68 is exposed in either orientation . referring now to fig6 , the layers 32 a and 34 beneath the patient &# 39 ; s heel 70 may be tapered to provide a downward slope 72 toward a foot end 24 of the mattress 14 on the upper surface of the mattress 14 and an upward slope 74 mirroring that of downward slope of 72 on the under surface of the mattress 14 so that in either orientation pressure on the patient &# 39 ; s heel against the mattress 14 is reduced in favor of pressure against a larger surface of the patient &# 39 ; s calf . referring now to fig7 , in one embodiment , the left and right edges of the foam layers 32 ( and 34 ) may optionally abut side bolsters 76 constructed of a high ifd foam , for example , having a value of 60 . the side bolsters 76 extend the full height and length of the mattress 14 and have a thickness of approximately 2 to 3 inches to provide stiff elements at the side of the mattress 14 that tend to cradle the patient away from the edges of the mattress 14 . the side bolsters 76 may be attached to the other foam layers and positioned inside of the fabric covering of the mattress 14 . an upper cover 80 may be constructed to be similar to the bottom cover 46 and to provide for left and right and foot and head tabs 82 extending away from a center panel 84 . each of the tabs 82 may include a hook and loop strip 86 attaching to a corresponding hook and loop strip 88 on the vertical walls of the cover 42 to retain the panel 84 against an upper surface of the mattress 14 . positioned on the left and right edge of the panel 84 near the left and right edge of the mattress 14 may be upwardly extending foam bolsters 90 that assist in retaining the patient centered in the panel 84 . the bolsters 90 may include a central foam element , for example , having a high ifd of 75 and may extend upward by approximately 5 inches . the bolsters 90 may be held against the upper surface of the panel 84 by a fabric covering 92 attached by stitching to the remainder of the cover 80 . in this way the bolsters 90 may be placed on either the soft face 18 a or the firm face 18 b according to how the mattress 14 is oriented . in either orientation of the mattress 14 , having the soft face 18 a upward or the firm face 18 b upward , the mattress 14 may receive a patient to provide a pressure redistributing surface suitable for sleeping and moderating high - pressure points which may lead to pressure ulcers or the like . the selection of the firmness of the exposed face of the mattress may be made according to a desire to control the concentration of pressure on the surface of the user &# 39 ; s body and / or to provide for support of the patient in the particular posture , for example , to alleviate back pain or the like . in addition , the firmness of the exposed face of the mattress may be selected to control the temperature of the interface between the patient &# 39 ; s skin and the mattress , with a firmer mattress , which is less enveloping , providing a cooler interface . in this regard , it will be appreciated that not only will different users prefer different firmnesses in the mattress , but that a single individual may wish to vary the firmness of the mattress at different times . a single mattress offering two degrees of firmness provides a substantial cost savings in both situations . it will be appreciated that other polymer foams may be used in lieu of polyurethane foam including for example latex foams and so - called “ memory foam ”. certain terminology is used herein for purposes of reference only , and thus is not intended to be limiting . for example , terms such as “ upper ”, “ lower ”, “ above ”, and “ below ” refer to directions in the drawings to which reference is made . terms such as “ front ”, “ back ”, “ rear ”, “ bottom ” and “ side ”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion . such terminology may include the words specifically mentioned above , derivatives thereof , and words of similar import . similarly , the terms “ first ”, “ second ” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context . when introducing elements or features of the present disclosure and the exemplary embodiments , the articles “ a ”, “ an ”, “ the ” and “ said ” are intended to mean that there are one or more of such elements or features . the terms “ comprising ”, “ including ” and “ having ” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted . it is further to be understood that the method steps , processes , and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated , unless specifically identified as an order of performance . it is also to be understood that additional or alternative steps may be employed . it is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims . all of the publications described herein , including patents and non - patent publications are hereby incorporated herein by reference in their entireties .
a mattress for institutional use provides upper and lower surfaces offering different levels of firmness through the use of gradiated firmness in multiple polymer foam layers .