Patent Publication Number: US-2011072589-A1

Title: Anatomical, pressure-evenizing mattress overlay with prestressed core, and baffled, lateral-edge core respiration

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/798,390, filed Apr. 2, 2010, for “Anatomical, Pressure-Evenizing Mattress Overlay and Associated Methodology”, which is a continuation-in-part of U.S. patent application Ser. No. 12/657,568, filed Jan. 21, 2010, for “Anatomical, Pressure-Evenizing Mattress Overlay”, which claims filing-date priority to prior-filed U.S. Provisional Patent Application Ser. No. 61/206,126, filed Jan. 28, 2009, for “Anti-Decubitus-Injury Mattress Overlay”. The entire disclosure contents of these three, prior-filed applications are hereby incorporated herein by reference. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention pertains generally to an anatomical, pressure-evenizing mattress overlay with a prestressed core, and baffled, lateral-edge core respiration windowing. More particularly, and with these generally-stated features solidly in place, it relates to a special-purpose, special-capability, breathable, friction- and shear-controlling, anatomical-support, pressure-evenizing, “mattress overlay” intended to be placed on top of, and used in conjunction with, an underlying, yieldable support surface, such as that provided by a mattress, for the purpose of furnishing “direct”, pressure-evenizing under-support for a substantially bed-ridden person. Respiration-window structure, and associated baffling, are employed to control cooling air-flow (gas-flow breathability) in the overlay-internal core structure for cooling and keeping perspiration-free a supported person, with the baffling also functioning to minimize (hopefully to prevention) the penetrating leakage of supported-person body liquid into that core structure. The concept of structural breathability, featured by the invention, is also intentionally referred to herein, pseudo-anagogously, in the language of “respiration”—a term most usually associated with human (or other animal) breathing. 
     In one of its important aspects, the present invention involves an improved version of the invention described in the above-referenced &#39;568 application, and in another important one of its aspects, it proposes an improved version of the invention described in the above-referenced &#39;390 application. 
     The overlay of the invention, in its preferred “thickness” configuration, is specifically designed, as will be explained more fully below, with a thickness (or thinness, depending on point of view) suitable, with the provision of appropriate, external yieldable under-support, for handling persons weighing up to about 350-lbs. In this configuration, it is definitively not designed to be used alone as a support on top of any rigid, underlying surface; nor is it intended to be a “stand-alone” support structure, such as a mattress, per se. 
     Where heavier persons are to be handled, such situation may be addressed either in the manner described in the above-referenced &#39;390 patent application, i.e., through the use of an external bariatric support structure, or may be accommodated differently, according to the present invention, by employing a herein illustrated and described, modified, plural-layer-core, thicker overlay structure which, for such a “heavy-handling” requirement, includes a different internal core formation that specially resists inadvertent, and problematic, “bottoming-out”. More will be said later about these ways of dealing with this especially heavy-weight, successful support matter. 
     For the more normal, “non-overly-heavy” supporting condition, the overlay proposed by the present invention, in its preferred and best-mode form, has a thickness which is no more than about 1-inches. This preferred thickness militates against its utilization respecting the “not-designed-for” uses just above mentioned. 
     The term “bed-ridden” as used herein as a “person characterization” is intended broadly to include a wide range of differently convalescing persons who may spend significant amounts of extended, body-support time not only specifically in hospital beds, but also on and in conjunction with other bed-like mattress structures. 
     Speaking with more particularity about the invention, and about what we see to be its remarkable, and experimentally demonstrated capability, it, the proposed “mattress overlay”, has as its special purpose the dramatic minimization of the onset and development of decubitus ulcers (sores)—medical conditions that lead to dangerous and potentially lethal injuries which come from long-term body-rest/support conditions. Accordingly, the overlay of the present invention is naturally, and particularly, well suited for placement on top of conventional, long-term, person/patient-support mattresses, such as hospital-bed mattresses. 
     With regard to use of the overlay of the invention on a conventional hospital-bed mattress, an interesting feature of the invention, which will be discussed more fully below, is its ability to stick relatively naturally, and without much potential for lateral slipping, on the surface of such a mattress on account of the fact that such a surface is typically defined by a smooth, gas- and moisture-impermeable, moisture-proof, mattress-body cover, such as a smooth vinyl cover. This propensity for overlay “stickage”, “or stiction”, discussed more fully later herein, results from a kind of distributed, “suction-cup” surface character which exists in the outer coating layer in the overlay owing both to the manner of coating fabrication and to the nature of the selected coating material, per se. Undesirable sticking to an overlay-supported person does not, for various reasons, occur. These reasons will also be identified later in this disclosure text. 
     While such a hospital-bed setting clearly presents an ideal use environment for the present invention, the defining term “mattress overlay” is intended herein to refer to any overlay structure constructed in accordance with the special and unique features of the present invention which may be shaped, sized, etc., for use not only on top of an underlying, conventional mattress structure, per se, but also in other similar environments where nonambulatory people, such as convalescing patients, may lie recurrently supported for long periods of time. The above-expressed concept of “direct”, underlying, person support, while it could (and can) include the concept of direct-to-skin contact support, herein more typically means support which is furnished, for example, (a) “directly through” clothing (such pajamas, a hospital gown, etc.), (b) through a bed sheet, or (c) through some combination of these and like things. 
     Regarding the above-mentioned special purpose of the present invention, it is now, and has been for some time, well recognized that the medical issue involving the development of decubitus ulcers in bed-ridden, etc., patients, often those people who are still in the environment of a hospital recovering from some medical event or condition, is an extremely serious problem—a problem which has recently caught the significant negative attention of medical-institutional (and related) insurance agencies who have come to recognize that prevention of the development of such ulcers is, in fact, quite possible, though through conventional approaches very challenging. This “negative attention” has translated itself, among other things, into agency refusals to offer/provide relevant insurance coverage. While the just-mentioned term “quite possible” is indeed true, real prevention—that is, effective real prevention—heretofore has been almost prohibitively expensive because of the fact that such prevention has, in reality, required substantial, frequent, personnel-intensive, one-to-one, or more-to-one, personal attendance to the changing of the resting “positions” of “bed-ridden” persons at risk. 
     The decubitus ulcer (decubitus-onset, decubitus-injury, decubitus-injury onset) problem is recognized today as being one of the most serious problems facing hospital and medical-care facilities, and these skilled care facilities are openly waging a fierce battle with state and federal agencies and insurance companies over who should pay the enormous costs in the treatment of this “new epidemic.” 
     In this setting, the prior art, of which we are aware, that has been aimed at addressing the “decubitus-injury” problem is rich with purportedly effective, proposed approaches for resolving it. In practice, none appears to be particularly successful or satisfactory, owing, as we perceive it, to the significant and apparent failure to grasp a comprehensive understanding of the key body-support environmental and contact conditions which must exist if decubitus “onset” is to be avoided, or at least significantly minimized. The present invention, we believe, “possesses” this understanding. 
     Presently known (to us), patent-related pieces of this prior art include: U.S. Patent Application Publication No. 2001/0034908 A1 of Duly, for “Mattress”; U.S. Pat. No. 5,031,261 to Fenner, Sr., for “Mattress Overlay For Avoidance of Decubitus Ulcers”; U.S. Pat. No. 5,077,849 to Farley, for “Anatomically Conformable Foam Support Pad”; U.S. Pat. No. 6,052,851 to Kohnle, for “Mattress For Minimizing Decubitus Ulcers”; U.S. Pat. No. 7,356,863 to Oprandi, for “Mattress Pad”. 
     While these identified, prior-art approaches address, and attempt to tackle with resolution, certain technical medical issues and conditions that can lead to the development of a decubitus injury (frequently referred to as a decubitus ulcer), clearly taking aim at successfully minimizing costly medical-personnel attention to “decubitus-at-risk” individuals, as far as we can tell, no one has successfully developed a truly effective support structure and/or methodology which has(have) the capabilities of substantially eliminating the likelihood that such a decubitus ulcer will develop. 
     The present invention changes this situation in a very pronounced fashion. While readings and study of this prior art, when compared with a reading of the present invention disclosure, may appear at first glance, and on certain points, to reveal only subtle differences, in reality these differences, in terms of substantially solving the problem of decubitus onset, are anything but subtle. Put another way, these differences “make the difference”! 
     While there are probably many issues that are usefully addressable in terms of preventing, or greatly limiting the possibility of the onset of, decubitus ulcers, the three, key considerations which we specially recognize in the characteristics of the present invention involve: 
     (a) (1) avoiding even very short-term (minutes) of high, applied anatomical pressure, (2) at all times pressure-evenizing the contact-loading characteristics which define how the anatomy of a bed-ridden patient is supported, and (3) specifically producing an anatomical loading condition, static and dynamic, whereby there exist substantially no notably high-pressure points (preferably none exceeding about 32-mm Hg, and even more preferably not exceeding about 20-mm Hg), and definitively no conditions involving a projecting portion of the person&#39;s anatomy (i.e., a protuberance) bottoming out against either a non-yielding, or relatively non-yielding, underlying support surface, or in any manner significantly raising (de-evenizing) anatomical support pressure; 
     (b) minimizing friction and shear engagement between the proposed overlay structure and a supported patient; and 
     (c), very importantly, providing effective, fluid-control-baffled, ventilating, heat-removing, perspiration-managing, cooling airflow (more broadly, cooling, gas-flow respiration) in the volumetric region disposed immediately beneath the supported anatomy so as to avoid the development of hot-spots and overheating, and especially recognizing that those portions of a supported anatomy, such as bony prominences, which create notable, downward “indentations” in an underlying support structure should be offered proportionally larger access to cooling air (gas) flow. 
     Stressing this just-identified, third, heat-removal and perspiration-managing, airflow-associated respiration concern, and repeating, with emphasis, the “proportionally” greater airflow comment just made above, it is especially relevant that the points/areas/regions of underlying anatomical support which must deal with the mentioned, notable, anatomical protuberances, and especially with pronounced (i.e., relatively “sharp”) protuberances, be designed to furnish locally enhanced, rather than more constricted, airflow within the anatomical support structure. Put another way such protuberance-support areas are the ones that potentially define the greatest risk for decubitus-ulcer development, and as we have discovered, are the areas where the most robust, ventilating airflow and air-circulation respiration capability need to exist. Generally speaking, the greater the size and/or “sharpness” of the protuberance, and thus the greater and the deeper and the more angular the resulting support-surface indentation, the greater the need for enhanced, support-structure airflow and air-circulation capability. 
     Unfortunately, known and proposed prior art manners of attacking the decubitus-ulcer problem do not recognize this special, anatomical-protuberance-support observation of ours, and failing that observation, actually propose supposedly problem-resolving body-support structures and associated methodologies which exacerbate the airflow respiration problem associated with protuberance support by reacting to downward protuberances with either no attention paid to airflow, or even worse, increased constriction to airflow. 
     With this background in mind, the present invention takes the form of an anatomical pressure-evenizing mattress overlay including (a) a dynamic-response, preferably uniform-thickness core expanse, or core, having spaced, upper and lower, surfaces and a perimetral edge extending between these surfaces, formed of a 100% open-cell, uniform-density compressible and flowable, viscoelastic foam, and having a “relaxed-state” volume in the overlay which is prestressed, by being about 8-10% compressed, to create a pre-stressed, pre-compression condition in the expanse, and (b) a differential-thickness (i.e., possessing different regions, or portions, of relative thickness, as well as regions, or portions, of relative thinness), elastomeric, vinyl coating having, due to such differential thickness, specifically different moisture-handling and gas-breathability, respiration-enabling, respiration windowing characteristics furnished importantly at different, selected locations in the overlay (as will shortly be explained). This coating, which is referred to herein as an at least partially gas-breathable coating, is load-transmissively, interfacially bonded to the entirety of the outside surface area of the core expanse to function as a dynamically-responsive unit with the expanse—with the coating possessing a “relaxed-state”, internal, prestressed tension condition which is responsible for the pre-stressed, pre-compression condition in the core expanse. 
     As will be seen, the mentioned core-expanse prestressing appreciably aids the critically important behaviors of core-structure respiration, and supported-person cooling. The term “relaxed-state” employed herein is used to refer to the conditions of the overlay components when the overlay is not in use. 
     The core expanse is intendedly and preferably formed of a specific-character, solid-phase, single-component, single-density, polyurethane material, shaped with its upper and lower surfaces substantially equidistant (i.e., the core expanse has preferably a uniform thickness) to give the overlay, as a whole, a substantially uniform thickness of no more than about 1-inches, with the differential-thickness coating having a lesser thickness (i.e., a portion, or portions, of thinness) of about 0.01-inches on certain respiration windowing regions of the overlay edges, and a greater thickness (i.e., a portion, or portions, of thickness) of about 0.02-inches elsewhere. These are all, certainly, dimensional matters of user choice, but they have specifically been found by us to be very useful, and consequently “preferred”. 
     Regarding the matter of differential coating thickness, two different, respiration-window-including, coating formations are proposed in different versions of the overlay that are described and illustrated herein. In one, the coating is defined with an elongate, continuous, diminished-thickness, respiration-windowing band (or, from another point of view, plural, elongate, end-connected, overlay-side bands) extending around the perimetral edge of the overlay. This band is also referred to herein as a perimetral band of thinness. The two, thickened, spaced, coating edges which define this band (or these bands) offer a respiration baffling function, are also referred to herein as baffle-function edges, and may be thought of as being a form of moisture-and-gas-control baffle structure. 
     In the other, the coating has, preferably, only a pair of very small, opposite-end (which may be thought of as “head-end” and “foot-end” parts of the overlay, though the overlay has no such specific “end” designations), edge-disposed, diminished-thickness portions, referred to as windows and as respiration window structure, each masked by a special, window-specific, moisture-and-gas-controlling baffle, or baffle structure. This special baffle structure takes the form of a sacrificial baffling assembly which offers a visibility, liquid-leakage, tell-tale function (relative to potential liquid leakage into the overlay core structure through the baffle-associated window structure), and, as will be later explained herein, is sacrificial in the sense that it is easily and repeatedly replaceable when such a leakage condition has been detected. 
     These relatively small respiration windows in this second-mentioned coating embodiment offer the additional, useful effect of promoting a kind of pneumatic resistance to core-structure compression as a supported person adjusts position on the overlay. 
     Accordingly, and for important structural and performance reasons which will be explained later herein regarding the coating, immediately outwardly (from the core expanse) beyond an initially created, overall primer sublayer (which flows bindingly into the core expanse material—an open cell foam material), the coating, distributed in an all-over configuration relative to the core expanse, is formed therefore on both the overlays&#39; perimetral edges and on its broad-surface areas, and specifically is preferably formed with ten, approximately 0.001-inches thick, cured, sublayers. These ten sublayers, further, are preferably spray-applied, one over another, under “wet-form”, interlayer bonding circumstances, where the “previously applied”, next-spray-receiving sublayer, including the mentioned primer sublayer (which adds substantially no depth to the coating, per se), is still wet and not yet cured. The ten sublayers define the “diminished-thickness” portions of the coating just mentioned above. 
     In some instances, less than ten, for example about six, sublayers may be used, resulting both in lesser material usage in overlay manufacture, and in somewhat greater respiration flowability, without appreciably diminishing needed overlay thickness. 
     Staying with the ten-sublayer construction for more detailed description purposes, different-thickness (greater-thickness) coating portions cover the two, broad-surface areas (each having what is referred to herein as an area A) in the overlay, as well as certain portions (differing in the two, different coating formations generally described above) of the overlay&#39;s perimetral edge regions. These thicker coating portions, which furnish moisture-shielding (impervious), core-protection, include outer, eleventh, individually thicker (about 0.01-inches) sublayers which are sprayed onto the immediately underlying, ten, thinner, “all-over, basic” sublayers after those underlying basic sublayers have dried. 
     The just-mentioned, wet-interlayer sublayer joinder methodology (and arrangement) employed in relation to the preferred, ten, basic sublayers in the coating produces, structurally, a final, cured, layered coating having, between substantially all next-adjacent, basic sublayers, and between the innermost, basic sublayer and the primer sublayer, what we refer to structurally herein as being finally cured, but initially wet, interfacial surfaces of joinder. We have found that this special type of wet, interfacial joinder structure enhances not only the gas-breathability characteristics of the overall coating, but also, importantly, the controlled shrinkage of the coating to produce the desired level of coating-internal tension, and core-expanse-internal compression. The one “area”, however, and as was just pointed out, of the prepared coating wherein the wet-interfacial joinder approach is not employed involves the application to each of the broad facial areas in the overlay of the final, eleventh coating sublayer. 
     Interestingly, and as was mentioned/suggested briefly above, when the outer layer has finally cured, it presents a special, exposed surface characteristic which outwardly presents an overall distribution of extremely tiny, i.e., essentially microscopic, suction-cup-like indentations. These indentations, quite by surprise, cause the overlay of the invention, when it rests upon the typically smooth, moisture- and gas-impermeable surface of the usual hospital-bed-mattress cover, to stick to that cover, through suction-cup action, tenaciously against lateral slippage. This sticking behavior furnishes a work-saving “blessing” to care personnel who must, as part of their “patient vigil”, be certain that an employed overlay remains properly in place beneath a supported person whose motion-restlessness might otherwise cause it to migrate precariously over the surface of its own undersupport. 
     Regarding the selectively differential gas-breathability aspects of the proposed coating (i.e., what may be thought of as being the coating “permeability-differentiating” features), the two (upper- and lower-face) broad-area regions of the coating in the overlay, and the extra-thickness coating sublayers which join with these broad-area regions at certain locations, are structured with their respective, eleventh, outermost, 0.01-inch-thickness sublayers formed so as to be substantially both moisture-impervious and gas-impermeable in nature, whereas the associated, ten, next-inner, “basic” sublayers are structured to be both moisture-resistant (but moisture-pervious) and gas-permeable. The “basic” sublayers, where not covered by the eleventh sublayer, function, in both of the described coating versions, as respiration windows to and for the core structure. 
     One practical and successful way of creating the coating to possess the mentioned sublayers with the respective, desired thicknesses and differential-permeability characteristics is set forth later herein. 
     The detailed description of the invention which follows below will describe fully the features of, and the importances attached to, the matters of core-expanse-material flowability, coating tension, core-expanse compression, coating-core-expanse mechanical binding to one another, and coating “permeability-differentiating” features. 
     The overlay, per se, which is elongate and generally planar in nature, and as has already been mentioned, has no preferential upper or lower end. Nor does it have any preferential top or bottom face, or side. It can, accordingly, confidently be placed with and in any suitable orientation on an appropriate supporting under-structure. 
     Functionally, and as will become very fully apparent, the invention features an overlay structure for furnishing pressure-evenized, dynamic-reaction support for the anatomy, which structure, in use, importantly supports the anatomy with a 100% open cell, polyurethane, viscoelastic foam that reacts to both static and dynamic, anatomical-unevenness-produced indentations in it to expand and contract foam-cell-openness size relatedly, whereby deeper and sharper foam indentations result in greater cell-openness size to promote significant, indentation-related core-structure air-flow “breathing” (i.e., respiration). Nominal compression in the core structure, and nominal tension in the coating structure, cooperate, and greatly assist this respiration behavior. 
     These and other features and advantages that are offered by the present invention will become more fully apparent as the detailed description which now follows is read in conjunction with the accompanying drawings. 
    
    
     
       DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  is a simplified, isometric view of an anatomical pressure-evenizing mattress overlay constructed in accordance with one preferred and best-mode embodiment of the present invention resting upon a fragmentarily shown hospital-bed mattress, and with a portion of one corner of the illustrated overlay broken away to illustrate details of internal construction. Components here are not necessarily shown to scale relative to one another. 
         FIG. 2  is a larger scale, fragmentary, cross-sectional view taken generally along the line  2 - 2  in  FIG. 1 . 
         FIG. 3  is an even larger-scale, fragmentary illustration of the region generally embraced by the two, curved arrows  3 - 3  in  FIG. 2 . 
       In  FIGS. 2 and 3 , it is also the case that the various overlay components are not necessarily drawn to scale. 
         FIG. 4  is a simplified, fragmentary view, drawn on about the same scale which is employed in  FIG. 2 , illustrating anatomical, load-bearing response of the overlay of  FIGS. 1-3 , inclusive, and especially showing how the dynamic-response core of the overlay of the present invention responds to such loading. What is shown in  FIG. 4  should be read along especially with what is seen in  FIG. 1 . 
         FIG. 5  is a simplified, fragmentary, isometric view in view of another preferred and best-mode embodiment of an anatomical pressure-evenizing mattress overlay constructed in accordance with the invention, this overlay also being shown resting upon a fragmentarily illustrated hospital-bed mattress. Portions of coating structure in this overlay have been broken away to reveal the internal core structure. This figure, which is drawn on about the same scale as that employed in  FIG. 1 , does not necessarily illustrate pictured components in correct proportions relative to one another. The embodiment pictured here includes both the above-mentioned, overlay-end-disposed, respiration window structure, and the also above-mentioned, special, sacrificial, tell-tale, respiration-window baffling structure. 
         FIG. 6  illustrates a pre-shaping, pre-installation preparedness condition of an isolated, respiration-window baffling assembly including a pair of baffle filter blocks and transparent adhering tape in their configuration and conditions relative to one another immediately before attachment of this assembly to form the lateral baffling structure, and an enclosed baffle chamber, for the respiration window structure which is pictured in and for the overlay shown in  FIG. 5 . 
         FIG. 7  is an enlarged-scale, fragmentary cross section showing a modified form of core structure in a modified overlay constructed in accordance with yet another embodiment of the invention, specifically showing an embodiment which is designed to handle large, overweight persons. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning attention now to the drawings, and referring first of all to  FIGS. 1-3 , inclusive, indicated generally at  10  is one preferred and best-mode embodiment of an anatomical, pressure-evenizing mattress overlay constructed in accordance with the present invention. Overlay  10  herein has an overall thickness of about 1-inches (a preferred maximum thickness), a lateral width of about 36-inches, and a length of about 75-inches. Each broad face of the overlay has an area A, not specifically labeled in the drawings. Overlay  10  is formed, basically, from two different components, or portions, including a single-piece, dynamic-response core expanse, or core,  12 , and a “differentiated character”, elastomeric coating  14  whose differentiated features, which relate to thickness, moisture-handling, and gas permeability/respiration (and consequently heat-removal handling) will shortly be described. Coating  14 , as will shortly be explained, is load-transmissively (mechanically), interfacially (face-to-face) bonded to the entireties of the outside broad-planar-facial and edge-surface areas of expanse  12 . The broad-planar-facial areas in core expanse  12  are shown at  12   a ,  12   b , and the edge-surface area, which is full perimetral in nature, is shown at  12   c.    
     In  FIGS. 1 and 2 , overlay  10  is shown resting upon a hospital-bed mattress of conventional construction shown generally, and fragmentarily-only, at  16  in these two drawing figures. The main body of mattress  16  herein is covered with a conventional, smooth-surfaced, gas- and moisture-impervious cover  16   a . As has been mentioned earlier herein, the mattress overlay of this invention need not necessarily be used in the setting of a conventional, hospital-bedding mattress, but may also be used, appropriately perimetrally shaped, to fit into other environments involving convalescing patients. In all instances, it is important that the mattress overlay of this invention be supported upon a mattress-like support structure, or other, similar, suitably yieldable understructure, in order to prevent core expanse  12  from bottoming out. Typically, though not necessarily, the overlay will be employed with a thin, fabric, sheet-like jacket to furnish a bed-sheet-like feeling to a supported person. 
     In this context, the about 1-inches thickness proposed herein as being preferable for the core expanse has been chosen for several reasons, one of which is that, when properly under-supported, and as above described, it will readily handle a person weighing about 350-lbs, and will also successfully deal, without bottoming out, with notably projecting, angular portions of the anatomy even involving persons of such weight. Under circumstances where an especially heavy person, for example someone who weighs more than about 350-pounds and up to about 500-lbs, is to be supported in accordance with practice of the invention, it is important that the overlay not be placed upon a hard and non-yielding undersurface, or be used alone as a mattress with stiff under-support. Such conditions could easily lead to undesirable bottoming-out. Rather, a modified form of the overlay, later to be described herein, should be used. 
     In addition to the mattress overlay of  FIG. 1  having, as a whole, a preferred thickness of about 1-inches in order to prevent a bottoming-out situation, another important reason for choosing an overlay thickness limited to about 1-inches in this embodiment of the invention is that this is a thickness which works well to assure maximum availability of the significant air-breathability capabilities of the selected overlay components. 
     According to one very important feature of the present invention, core expanse  12  is formed of a 100% open-cell, single-density, viscoelastic foam, most preferably made from the product known as #5010 CF Visco, polyurethane, Domfoam made by Domfoam International, Inc. in Montreal Quebec, Canada. This foam is both compressible and flowable. Significantly, this foam which has been chosen for the core expanse has another, very important, internal structural character whereby, under changing compression-pressure conditions, it exhibits a compressive-deflection vs. compression-force (or load) curve which includes an extremely linear region over which a relatively wide change in compressive deflection is accompanied by what turns out to be an anatomically insignificant (i.e., only slightly perceptible) change in compression pressure. This feature plays a very important role in assuring evenized support pressure applied statically and dynamically to the underside of a supported anatomy, notwithstanding the presences of, say, any bony anatomical protrusions. 
     For a reason which will now be explained, and as has already been mentioned above, core expanse  12 , within the overall structure of overlay  10 , is in a pre-stressed compressed condition, with a “relaxed-state” compression internally of about 8-10%. This compression is brought about by virtue of the presence of allover overcoating by coating  14  which is a multi-sublayered, sprayed-on, elastomeric, vinyl coating prepared with a “varied” overall thickness, as was mentioned earlier, and as will be more fully explained shortly, lying preferably in the range expressed earlier herein of about 0.01-inches to about 0.02-inches. Coating  14  preferably is made from a vinyl material such as that manufactured and sold by PlastiDip International in Blaine, Minn. under the identity Miraculon PDF-830. As was also mentioned earlier herein, coating  14  is prepared, illustratively and preferably, and in certain different regions of the coating, with different pluralities, and different, overall thicknesses, of sublayers, most of which (i.e., the “basic” sublayers), individually, have thicknesses of about 0.001-inches, and a few of which have the greater sublayer thickness which is employed herein of about 0.01-inches—these different sublayer pluralities and thicknesses accounting for the coating&#39;s “varied, or differential, thickness” nature. 
     The coating is formed, almost throughout, in a special manner to ensure several important structural and performance features. One of these features is that, except in those coating regions included in the broad-area portions of the overlay, and in thicker-coating portions of the perimetral edge regions of the overlay, a special, inter-sublayer joinder exists between each of the sprayed-on sublayers to improve moisture-handling, gas-breathability, and attendant heat-removal and perspiration-management capabilities of the coating. Another of these features is that the coating, when completed, demonstrates a controlled shrinkage which is responsible for placing core expanse  12  into nominal, overall compression, and the coating into a nominal prestressed, tensed condition. 
     In the just-mentioned, broad-area and perimetral-edge thicker portions of the overlay, a different inter-sublayer joinder structure exists between the outermost sublayer, and the immediate next-inner sublayer. This will be more fully described shortly. 
     In the embodiment of the invention now being described, the coating-structure regions which cover facial areas  12   a ,  12   b  in the core expanse, as well as those which cover certain (upper and lower as seen in  FIGS. 1 and 2 ) portions of perimetral edge area  12   c , have outer sublayers that differ somewhat in construction from that of the outermost sublayer regions of coating  14  which cover the vertically central, “horizontally elongate”, clearly visible, band-like, or band, portions of perimetral edge area  12   c  in the core expanse. 
     Directing attention specifically to  FIGS. 2 and 3 , here fragments of core expanse  12 , and of different portions of the plural-sublayer construction of coating  14 , are illustrated. Coating  14  includes (a) two, broad-area, about 0.02-inches-thick, facial portions  14 A which extend over and cover facial areas  12   a ,  12   b  in core expanse  12 , (b) two, elongate, vertically spaced, 0.02-inches-thick, perimetral edge stretches  14 B which extend over and cover spaced upper and lower parts of perimetral edge-area  12   c  in the core expanse, and (c) an elongate, vertically central, about 0.01-inches-thick, perimetral edge band  14 C which extends over and covers that portion of the core expanse&#39;s perimetral edge-area  12   c  which lies between coating stretches  14 B. The vertical dimensions of coating stretches  14 B, and band  14 C are substantially equal with dimensions each of about ⅓-inches—the term “vertical” herein relating generally to the orientations of  FIGS. 2 and 3 . 
     Coating stretch  14 C may be thought of as being one continuous, elongate, overlay-perimetral band of thinness in the coating, or as an endo-connected collection of overlay edge-side-specific, plural bands of thinness therein, and this stretch is referred to herein as a window, as a respiration window structure, and as a baffled, respiration window structure. The spaced, confronting edges of coating stretches  14 B which evidently define this band-like window structure are referred to herein also as baffle-function edges which laterally baffle the associated window structure to control fluid flow (liquid and gas) through the window structure into and out of the core expanse. 
       FIG. 3  illustrates, more particularly, the respective constructions of coating portions and stretches  14 A,  14 B,  14 C. 
     Each of these three coating portions/stretches commonly includes (1) a primer sublayer  14   a  (shown in dashed lines) which has penetrated the adjacent outer portion of core expanse  12 , and which adds no appreciable thickness to the coating, and (2) ten, joined, thin, “basic” sublayers, such as the two, basic sublayers shown at  14   b . An interfacial bond (of the special, “wet-form” nature mentioned above), one of which is shown by a heavy line  14   c  in  FIG. 3 , exists between each of these just-mentioned primer and “basic” sublayers. This special interfacial bond is referred to herein as being defined by “initially wet”, interfacial surfaces of joinder. 
     Coating portions  14 A and stretches  14 B, alone among the regions in coating  14 , include the previously-mentioned, additional, eleventh, thicker outer sublayer, such being pictured at  14   d  in  FIG. 3 . Sublayers  14   d  in these coating portions and linked stretches form, in coating  14 , a kind of cap, or capping structure, which “receives”, to about one-third each the overall core-expanse thickness, the opposite facial zones in the core-expanse structure. Such capping structure(s), and particularly the edge stretches therein, define the above discussed, laterally vertically-central breathing and moisture-venting respiration window band, or bands in the overall overlay structure. 
     Coating region  14 C includes only the combination of primer sublayer  14   a  and each of the ten, basic, thin sublayers  14   b.    
     A consequence of this construction is that coating portions  14 A and stretches  14 B preferably have overall thicknesses herein of about 0.02-inches, whereas coating portion  14 C has preferably an overall thickness of only about 0.01-inches. 
     As illustrated in  FIG. 3 , whereas all of the sublayers that are there pictured within the illustrated coating portions have been shaded similarly to make them easily readable as individual sublayers, outer, thick sublayer  14   d  is different internally, in that it is constructed to have somewhat different gas-permeability and heat-removal behaviors than those like-character behaviors of each of the next ten, other, underlying sublayers. More specifically, sublayer  14   d  has-been prepared so as to be, essentially, both moisture-impervious and gas-impermeable in nature, whereas the next ten, underlying, other sublayers, the so-called basic sublayers, have been prepared differently so as to be moisture-resistant (i.e., not impervious to moisture) and gas-permeable in nature. 
     Describing now the process preferably employed to create the different sublayers in the different regions, or portions, of coating  14 , generally speaking, there are two, different spraying arrangements which are used during coating creation. One of these involves supporting a flat expanse of “material” (i.e., either an initial, not yet in any way coated, flat expanse of the mentioned core material alone, or, a flat expanse of partially coated core material) on a generally horizontal table, and producing linear, repetitive, plural-cycle relative motion between an overhead plurality of appropriately laterally and vertically spaced/distanced spray heads and the material-supported material expanse. This is preferably accomplished by holding the table and supported material stationary, and moving the spray heads. The other arrangement involves supporting a material expanse (by this time partially coated, as will be explained) in what might be a somewhat clamp-like jig, and producing relative rotational motion between the so-supported expanse and, typically, a single spray head, appropriately distanced so as to create the perimeter edge portions of the desired coating. 
     Preferably, spraying takes place, utilizing conventional Devilbiss spray-equipment spray guns (or spray heads) each with a #704 cap and a 0.055 spray tip and needle, in an environment which has a temperature of around 65° F., with a blend of air and the above mentioned Miraculon spray product supplied for spraying at the same temperature which is essentially. Environmental humidity preferably lies at about 25%. Throughout spraying, air and Miraculon are supplied to the spray-heads at respective flow pressures of 80-psi and 50-psi. As will be pointed out below, during different steps of spray-application, spray gun control valves are operated variously either fully open with respect to the supply of Miraculon, or “throttled down” to substantially ⅓-open conditions. 
     Further describing general spray-application conditions, it is preferable that the spray heads be disposed at a distance from the “target structure” by about 10- to about 12-inches, with the spray head organization which is employed during spraying broad-expanse areas of “target structure” being spaced by a distance whereby their respective sprays, where these strike the target, overlapping one another by about 50-percent. It is also preferable that relative (liner and rotational) motion, depending upon where spraying is taking place, at the rate of about 3-inches-per-second, be used between the spray-head structure and the structure being spray coated. 
     Coating preparation begins by placing a not yet edge-sized, i.e., not yet perimeter-sized, expanse of the above-mentioned Domfoam material on a horizontal table, and by then applying to the exposed broad surface area of the expanse, and first of all, a primer sublayer  14   a  of Miraculon material with the valves in the spray-heads fully open, and with “primer spraying” occurring in a single pass over the mentioned, exposed expanse area. This primer sublayer soaks into the Domfoam expanse to create a tenacious, mechanical bond directly with that expanse, leaving a wet surface exposed on the face of the expanse, but exhibiting no appreciable “external” depth (i.e., outwardly of the core expanse). 
     This primer sublayer spraying is immediately followed, while the primer sublayer material is still wet and uncured, with ten, successive next-adjacent-sublayer spray-head passes over the same, exposed expanse area, with the only difference being that the spray-head valves, in each pass, are throttled down to their above-mentioned ⅓-open conditions. Each of these next ten spray passes follows the immediately preceding pass while the last-applied sublayer is still wet and uncured to create the “wet-form”, inter-sublayer bonds  14   c . Each of these next, ten, “throttled-down”, “wet-interface” passes produces a Miraculon sublayer  14   b  having a thickness of about 0.001-inches, and which is characterized with a quality of open “stringiness”. 
     Following the procedure which has just been described relative to one broad surface of a Domfoam expanse, a spraying is paused for a period of about 30-minutes to allow the layers of material that have just been sprayed to dry and cure more thoroughly. Thereafter, the expanse is turned over and the process just described is repeated in its entirety to create a similar multi-sublayer coating on the opposite broad face of the expanse. This repeated procedure is followed by a similar pause in spraying as was just mentioned. 
     Thereafter, the Domfoam core expanse, which now has, on its opposite, broad faces, an almost completed coating (complete except for missing just the final, eleventh, thicker outer sublayer  14   d ), is allowed to “rest” for about 24-hours to enable all then-applied basic sublayers to cure substantially, and is then appropriately trimmed to have the correct perimetral outline. 
     The perimeter-trimmed expanse is next placed in a suitable supporting jig, which may take the form of a broad-platen clamping jig, for controlled relative rotation, first, in a single rotation cycle past a spray head (which is fully open) to apply an edge primer sublayer  14   a , followed in quick succession by ten additional rotation cycles (with the spray head throttled down to a ⅓-open condition) to apply the intended, ten, edge-coating, wet-bonded sublayers  14   b . Spraying is now paused for the same, above-mentioned, about 30-minute time interval, and for the same reason. 
     At this point in the coating process, the coated structure which has been created so far is broad-surface supported on a horizontal table, one side at a time, and sprayed on each broad surface with the spray heads in fully open conditions, and in a single spray pass per side, to create the required, about 0.01-inches thickness, final, eleventh, outer broad-area coating sublayers  14   d . A spraying pause interval, here of about 24-hours, is interposed the spraying of these two broad surfaces. 
     What next occurs is that, effectively for each edge of the overlay structure formed so far, and with that partially completed overlay structure resting in a substantially horizontal plane, an elongate, about ¼-inch-diameter, metal (or plastic) rod (or the like) is suitably supported in a condition substantially horizontally disposed, parallel to and closely adjacent the edge, and vertically centered relative to the upper and lower broad faces of the structure, so as to furnish a “spray-shadow” mask which will be employed now for the purpose of assisting in the creation, along the relevant edge, of the two, separated, upper and lower coating stretches  14 B, and the associated, separating edge band  14 C. This “rod-masking” may be performed (for spraying) either (a) on an edge-by-edge, single-edge basis, or (b), for all four edges “at once”, utilizing a masking rod for each edge, or even a single, suitably sized and angled, single, “bent”, circumsurrounding rod. 
     With rod-masking in-place, and with the overlay structure suitably supported, along with the masking rod structure, in a jig of the type generally mentioned earlier herein, a single spray pass (per edge) of the type generally employed to create just-described, thick coating sublayers  14   d  is implemented to create, around the perimetral edge of the structure what may be thought of as angularly intersecting, continuation portions of previously created, broad-surface-area layers  14   d , in order to create the differential-thickness coating structure which is clearly illustrated in  FIG. 3  in the drawings. 
     After this final edge spraying has taken place, the rod-masking structure is removed, and the entire, and all of the various spray sublayers in the now fully spray-coated core expanse are allowed to cure and dry even more thoroughly in an environment whose temperature is about 95° F., and for a period preferably of about 3-5-days. 
     When sublayer spraying takes place in accordance with these just mentioned and described, different spray-application (parameter) considerations, the various sublayers evidence the desired, differentiated gas-handling and moisture-permeability characteristics generally described for them above. A clear consequence of this coating-creation procedure is that different regions in the coating behave differently. In the two, broad-area portions  14 A, and the two, vertically spaced, perimetral, edge portions (stretches)  14 B, of the coating, as far as the “outside world” is concerned, relative to the overlay&#39;s internal core expanse, there is a substantial moisture and gas-flow, impermeability barrier. Immediately inwardly in these two areas, however, i.e., immediately inwardly of the outer coating sublayer  14   d  in these areas, there is gas-breathability within the basic-sublayer, internal portions of the coating extending inwardly to adjacent the core expanse. In the vertically central, perimetral edge areas (band)  14 C of the coating, there is moisture resistance (but not impermeability), and gas-breathability, through and throughout this portion of the coating structure and in communication with the core expanse. 
     These important coating considerations result in several significant overlay conditions and behavioral features. In particular, the resulting structural joinder which develops in the interfacial regions between the individual, basic sublayers in coating  14  offers improved gas-breathability in the relevant regions mentioned above in the final structure of coating  14 , and further, promotes appropriately controlled shrinkage of coating  14  as a whole to create the different pre-stressed compression and tension conditions mentioned above for the core expanse and the coating, respectively. 
     Thin application of at least the first-to-be-sprayed-on (i.e., core-expanse-contacting) primer sublayer regions in coating  14  causes the coating as a whole to bond robustly mechanically (in a manner which we refer to as load-transmissively) to the entire outside surface area of the core expanse, with the result that the localized regions of joinder of the core expanse and the coating function essentially as a unit everywhere within the overlay. 
     As mentioned briefly above, a surprise to us resulting from the coating process which has just been described is that the outer coating layer  14   d , on curing, develops over its entire outside surface a distribution of tiny, essentially microscopic, suction-cup-like dimples, or suction cups.  FIG. 1  in the drawings generally, schematically, and entirely out of scale, illustrates this surface condition at  17 . These dimples furnish the earlier-herein-mentioned anti-migration stiction which the overlay of the invention advantageously demonstrates when it is placed on a smooth support surface, such as that offered by the usual vinyl cover provided for a hospital-bed-like mattress. 
     Adding reference now to  FIG. 4  along with the other drawing figures, this bonding condition produces an “in-use” action, extremely important in the behavior of overlay  10 , wherein expansive stretching of the coating, such as that which occurs, for example, when the anatomy, and particularly a sharp, anatomical protuberance therein, depresses the overlay support surface (see representative arrow  18  in  FIGS. 1 and 4 ), pulls on the bonded core expanse, and causes (a) core-openness size in that pulled-on and resultingly expanded, core-expanse region to enlarge, and (b) airflow openness in at least the innermost sublayers in the coating to increase locally, thus immediately promoting increased airflow capability and activity in that region. Prestress compression in the core expanse importantly aids in this action, since that compression urges the core expanse to swell non-resistively, and expand. When the protuberance represented by arrow  18  engages the overlay, and with an understanding that things are purposely illustrated exaggeratedly in  FIG. 4 , it produces a significant depression  14 D in coating  14 , and a matching depression in the upper surface of core expanse  12 . Given the modest thickness of the core expanse, this depression “telegraphs” its presence to some extent to the immediate underside of the expanse to produce the gentle downward bulging in coating  14  shown at  14 E. 
     This “depression/bulging” condition is characterized, of course, by an expanding and stretching of the coating at the  14 D,  14 E locations therein, and attendant increasing of the there-local airflow permeability of at least the internal sublayers in the coating. This expanding and stretching, in addition to producing an interesting and effective, internal, “bellows” air-flow condition, causes related, outward, lateral “dragging” of the bonded core expanse, aided in that “dragging” by the relaxation of compression in that expanse. The squeezing which results in the core expanse between locations  14 D,  14 E produces slight, lateral, outward flowing of the expanse as indicated by arrows  20 ,  22 , with outwardly flowed core expanse-material represented in the two, angular, lightly shaded region of that expanse shown at  24 .  26 . 
     Further considering air-flow (gas-flow) management features of overlay  10 , particularly with reference to how the broad-area and vertically central, perimetral-edge regions of the core structure perform, the fact that the thicker, outer sublayers  14   d  in the coating are, effectively, gas-impermeable, depressions and relaxations of depressions which occur in the overlay, for example as a person supported on the overlay moves from time to time, recurrently create the just-above-mentioned kind of bellows air-flow effect within the inside of the overlay, forcing air to flow inwardly and outwardly through the gas-permeable (breathable) band portion(s)  14 C in the coating. 
     It is these, several air-management features of the invention, promoted by relative thinness in the overall overlay, by the mechanical bondedness which exists between the core expanse and the coating, by the coating structure, and by the pre-compression/pretension conditions extant in the core expanse and coating, respectively, which cause the overlay to adapt needed anatomical-support airflow, and associated heat removal and perspiration-management, in a manner whereby those supported areas of the anatomy which should receive enhanced, cooling airflow in the context of being protected against “decubitus onset” do receive such enhanced treatment. This adaptation behavior is dynamic, in the sense that changes in supported anatomy position are followed appropriately and instantly in the context of most-needed airflow availability. 
     We have also discovered that the thicker, outer coating sublayers in the overlay, on one of which a supported user will always be lying, aid in heat removal—transferring excess heat to the interior of the overlay, wherein air flow functions to discharge it laterally outwardly through the edges of the overlay. These same outer, thicker sublayers play an important role in minimizing friction and shear engagements with the anatomy of a supported person. Such engagements are also naturally minimized by the presence of any fabric which may be interposed the overlay a supported anatomy, as well as by the fact that the outer surface of coating layer  14   d  does not have a tendency to stick to the skin. 
     Prior art structures that are known to us have no such capabilities for offering this important decubitus-injury-minimizing behavior. In many instances, unfortunately, prior art structures often respond to support indentation in a harmful manner which closes off support-offering airflow capability the deeper/larger the indentation which exists. 
     Regarding a certain aspect of moisture management, the moisture-impervious character of the thicker, outer broad-area and lateral-edge sublayers in the coating tend to inhibit external moisture entry into the core expanse, including, importantly, along the lateral margins of the overlay. 
     The overlay embodiment which has been described so far herein has been found to perform very satisfactorily in many applications and situations, but there are certain environments in which it has been determined to be important that the overlay furnish an even greater control over respiration-window access to the central core structure, particularly to minimize, as close to zero as possible, the likelihood that body fluids from a person resting on the overlay might work their way through the respiration window structure into the 100% open-cell foam core expanse. 
     Accordingly, while the overlay configuration pictured specifically in  FIGS. 1-3 , inclusive, affords generally adequate fluid-flow, and particularly liquid-flow baffling to prevent such liquid seepage/leakage into the core expanse, another important and preferred embodiment of the invention, now to be described, more definitively controls the prevention of such an event, i.e., liquid leakage. This alternative embodiment, which offers the most robust “anti-leakage” control is illustrated in  FIGS. 5 and 6  in the drawings, to which attention is now specifically directed. 
     Indicated generally at  30  in  FIG. 5  is a mattress overlay which is constructed in accordance with the features of the alternative embodiment of the present invention just mentioned above, and now to be described. Overlay  30 , which possesses a long, central axis  30 A, is pictured in a condition wherein it is supported on a conventional hospital-bed mattress shown fragmentarily at  31 . 
     In many ways, overlay  30  is substantially the same in construction (sizes, i.e., dimensions, and materials) as previously described overlay  10 , with the exception that, while its core structure is essentially identical, and its coating-structure layer-arrangement is also essentially identical, its coating-provided respiration window structure, in terms of size, location, and fluid-flow-control baffling, is quite different. 
     Continuing, included in overlay  30  is a core expanse  32  having (as was just mentioned) the same material construction, dimensionality, and functional features as those described for previously discussed core expanse  12 . Core expanse  32 , also referred to both as a core structure and as a core, is coated by a multi-layer/sublayer coating, or coating structure,  34  which, in terms of its specific layer arrangement, its layer formation by spraying, and its layer dimensionality, is identical (as was also just mentioned) to previously described coating, or coating structure,  14 . 
     Because of the substantial structural identities just mentioned between the two core expanses, and between the layer/sublayer arrangements in their respectively associated coating structures, we do not repeat here any detailed descriptions of these structures—focusing attention instead on how coating structure  34  in modified overlay  30  is specifically configured differently to create the different form of overlay-end-disposed respiration window structure mentioned generally above. 
     What specifically distinguishes the comparative constructions of overlays  10  and  30  is that, whereas in overlay  10 , the included, baffled respiration window structure takes the form, effectively, of an endless, elongate, thin-coating-region band extending perimetrally around the outside of the overlay, as described above, the baffled respiration window structure in overlay  30  takes the form of a pair of relatively small, rectangular windows, such as the window seen at  36  in  FIG. 5 , one each formed adjacent the opposite, long-dimension ends of the overlay. Because of the fragmentary nature of what is shown in  FIG. 5 , only one of these two windows is pictured in the drawings. Window  30 , and its counterpart located adjacent the opposite (and unseen) end of overlay  30 , is basically defined as a rectangle (as mentioned) formed in the outer, thicker layer, of coating  34 , with the coating-layer edges that define this rectangular window furnishing a portion of the lateral baffling which exists for each of these windows. These windows herein have lateral dimensions of about 1-inch by about 1.75-inches. 
     The adjacent, thicker and thinner regions in coating  34  which define window  36  are similar to what is illustrated in enlarged, cross-sectional detail in  FIGS. 2 and 3  for the adjacent, thicker and thinner regions in coating  14 , and these two  FIGS. 2 and 3 ), accordingly, may correctly be viewed as furnishing a closer, and more detailed, “picture” of the structure of window  36  than that which is presented for it more generally, and distantly, in  FIG. 5 . 
     While different specific dimensionality may be chosen for the windows, such as for window  36 , a particular dimensional ratio in overlay  30  has been determined as one which furnishes very satisfactory respiration breathability for the core expanse in the overlay, while at the same time minimizing overall window size to inhibit the likelihood of liquid leakage into core  32  should any such leakage liquid get past the foam filter blocks. This ratio relates the surface area of one broad side of the overlay to the combined areas of the two windows, such as window  36 . More specifically, in accordance with this special ratio, where the overall surface area of a single broad side of the overlay is given by the variable A, the combined surface areas of the two windows, should equals about 0.0013 A. 
     Focusing attention now specifically on the region in overlay  30  which is immediately adjacent respiration window  36  as seen in  FIG. 5 , directly, structurally and functionally associated with this window is important, additional baffling structure, referred to also herein as tell-tale-functioning, sacrificial baffling structure, which takes the form of a baffling assembly  38 . Assembly  38  includes a pair of laterally spaced, breathable, foam filter blocks  40 , referred to herein as baffle-filter blocks, disposed slightly spaced from, but positioned generally relatively closely adjacent, the laterally opposite sides of window  36 . These blocks, which have nominal (i.e., before an assembly  38  is installed, as will shortly be explained) rectilinear configurations with dimensions of about 1×1×  1 / 2 -inches, are held in place in the overlay by an expanse of transparent, moisture- and gas-impervious adhering tape  42  having an adhesive side which attaches to the two foam blocks, and to the clearly illustrated surface regions adjacent window  36  on the opposite broad surfaces of coating  34 . As will also shortly be explained, attachment of the baffling assembly to coating  34  to have the appearance seen in  FIG. 5  produces the outwardly projecting, dome-like “rounding”, or out-of-rectangularity distortion, in those sides of the blocks which generally face the viewer in  FIG. 5 . 
     Blocks  40  and tape  42  collaborate to form the entirety of assembly  38 , and collectively define an enclosed, moisture-passage barriering, but gas-respiration-breathable, baffle chamber  44  disposed in communication with, and on the outside of, window  36 . As can be seen in  FIG. 5 , baffle chamber  44  is defined, on its laterally opposite sides, by blocks  40 , on its inner side by the overlay edges of coating  34  which lie between these blocks and which include window  36 , and on its outer side, which faces generally toward the viewer in  FIG. 5 , by tape  42 . 
     This same kind of baffling assembly is present (though not seen in the drawings) adjacent the other, end-disposed respiration window structure in the overlay. Preferably, though not necessarily, the two respiration window structures, such as window structure  36 , and the two, associated baffling assemblies, such as assembly  38 , are positioned somewhat to one side of the longitudinal centerline,  30 A, of the overlay to avoid any damage to these structures in the event that the overlay is folded along this centerline for storage, or for any other reason. This positioning condition can clearly be seen for these structures in  FIG. 5 . 
     Preferably, the foam filter blocks are formed of the same material which is employed in core expanse  32 , and the adhering tape is formed of 3M #8672 8-mil vinyl tape made by the 3M Corporation. Also preferable is that the color of the specific foam material employed in blocks  40  be light in color (such as white or off-white), so that these blocks will function, via discoloration which will be visible through the adhering tape, as “tell-tales” to signal the occurrence of any liquid leakage which may be attempting to reach the margins of the baffled respiration window. 
       FIG. 6  in the drawings illustrates, as mentioned above in the description of this figure, a pre-shaping, pre-installation preparedness condition for baffling assembly  38 . Here, what can be seen is that a piece of appropriately sized tape  42 , with its adhesive side appropriately exposed and upwardly facing in this figure, has placed upon it, near a pair of its lateral margins, as illustrated, and with the dispositions pictured, two, foam, baffle filter blocks  40 , each of which, as was also mentioned earlier herein, nominally has a rectilinear block shape. Also placed upon it, in order to cover the tape&#39;s adhesive surface which would otherwise be openly exposed in the rectangular zone residing between blocks  40 , is a thin, transparent-material film  45  (shown only fragmentarily). Film  45  prevents this zone in the tape from inadvertently attaching itself to the portions of the outer coating in the overlay that are exposed within baffle chamber  44  in a manner which might partially, or completely, seal window  36 . 
     With this pre-installation condition established, the assembly is suitably curled, as indicated by arrows  46 ,  48 , and placed appropriately in juxtaposition to one of windows  36 , with suitable tension introduced into tape  42  in the installation process to compress and reform the filter blocks so that they take on the outwardly projecting domed shapes which are pictured clearly for them in  FIG. 5 . 
     The adhesive material which forms part of tape  42  is “non-damaging” in relation to coating  34 , and as a consequence, this allows a baffling assembly, in its “sacrificial” mode of operation, namely, once there may be indicated a fluid leak which has discolored one or both of the filter blocks, easily to be removed for replacement by another, similar, baffling assembly. Transparency in tape  42  easily enables one to see, by a looking for discoloration in the preferably lightly colored filter blocks, any indication that an undesired liquid leak has taken place, or has begun. 
     Where it is desired that the overlay of the present invention be employed with a person whose weight lies in the range, for example, of about 350-lbs to about 500-lbs, two different handling approaches, generally mentioned earlier herein, may be employed. In one, a suitable, independent, bariatric, under-support structure may be used. Preferably, such an under-support structure will have essentially the same perimetral outline as that of the supported overlay, and will furnish appropriate yieldable under-support to prevent bottoming out of the core expanse in the supported overlay. While many different kinds of such bariatric under-support structures may be employed, we have experimented successfully with a 1-inches thick pad formed of two layers of different, rate-sensitive, viscoelastic foam materials specifically made by AEARO Specialty Composites in Indianapolis, Ind., with an upper layer in this pad having a thickness of about 0.75-inches and being formed of the material sold as Confor CF-42 foam, joined by adhesive bonding to a lower layer of the material sold as Confor CF-45 foam having a thickness of about 0.25-inches. There are, of course, many other materials which may be employed successfully for such a bariatric under-support structure. 
     Another approach is illustrated in  FIG. 7  in the drawings generally at  50  which pictures another modified version of the overlay of the present invention. Overlay  50 , as proposed herein, includes an overall thickness of about 2-inches, and is formed with a plural-layer core, or core structure,  52  formed with a ½-inches thick underlayer  54  of the above-mentioned Confor CF-45 foam material, suitably adhesively bonded to an intermediate layer  56  of the above-mentioned Confor CF-42 foam material, also having a thickness of about ½-inches, and with layer  56  being suitably adhesively bonded to a layer  58  having a thickness of about 1-inches, formed of same core-expanse material previously described herein for expanses  12 ,  32 . 
     Overlay  50  further includes an overall coating  60 , which is substantially identical in layer arrangement to the coatings which have already been discussed herein. Coating  60  includes a pair of baffle-chambered respiration windows (not specifically shown) which are like those that have been described for the invention embodiment of  FIGS. 5 and 6 , such respiration windows essentially being formed so as to expose only core layer  60 , generally at opposite ends of overlay  50 , and occupying regions generally illustrated at W in  FIG. 7 . 
     Thus the present invention, now described in several preferred embodiments, offers an anatomical pressure-evenizing mattress overlay including (1) a core, in different-modification forms, with each modification form possessing a dynamic-response core expanse having spaced, upper and lower, surfaces and a perimetral edge extending between these surfaces, the core expanse being formed from a 100% open-cell, compressible and flowable, viscoelastic foam, and having a relaxed-state volume in the overlay which is prestressed, and about 8-10% compressed, thus to create a pre-compression condition in the expanse, and (2) an elastomeric, moisture- and gas-flow-managing, specially baffled, respiration-windowed, coating, load-transmissively bonded to the entirety of the outside of the core expanse to function as a dynamically-responsive unit with the expanse, and possessing a relaxed-state internal prestressed tension condition. 
     Within this structure, the core expanse exhibits a compressive-deflection vs. compression-force curve which includes an extremely linear region over which a relatively wide change in compressive deflection is accompanied by an anatomically insignificant change in compression pressure. 
     Accordingly, a unique mattress overlay structure which is aimed with a very particular focus on helping to resolve the decubitus ulcer/injury problem have thus been illustrated and described herein, with certain variations and modifications suggested. Among the important factors relating to resolving this very dangerous and widespread kind of injury, namely, (a) paying close attention to furnishing support for the anatomy with an overall, evenized pressure which falls within a certain, identified range of pressures, (b) controlling and minimizing friction and shear conditions in the interface between the overlay support structure and the anatomy, and (c), extremely importantly, furnishing adequate cooling airflow to the supported anatomy via respiration window structure which is specially baffled to control both air(gas)-flow, and liquid-leakage, all are dealt with effectively by the present invention. 
     As has been pointed out with great particularity, the unique structure of the present mattress overlay includes a special core foam material which is completely 100% open-celled in nature, and which is nominally under compression, coated by a differential-thickness, moisture- and gas-managing elastomeric layer which is bonded tenaciously (interfacially, mechanically bonded) to surface areas of such core foam. This unique collaborative union of structures results in the occurrence of a very special performance regarding anatomically-cooling airflow, wherein the deeper the indentation produced in the overlay by a portion of the body supported on it, the greater the “effective openness” of the supporting core foam material to enhance airflow in the region, or regions, of such indentation, or indentations. 
     In conclusion, while a preferred and best mode embodiment of, and manner of practicing, the present invention have been illustrated and described herein, and certain variations and modifications suggested, we appreciate that other variations and modifications may be made without departing from the spirit of the invention, and it is our intention that all of the claims to invention will be construed as covering all such other variations and modifications.