Two layer pack structure with offset seams
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to soft pack structures such as stuffsacks, backpacks or rucksacks adapted to contain articles for transport, and more particularly to a soft pack structure having enhanced integrity against water infiltration, the structure including a substantially conventional outer pack structure of pliable water resistant material having an opening defined therein and means to close and cover such pliable opening, and an inner bag structure also of water resistant, pliable material adapted to fit within the outer pack structure and cooperate with the closure means of the upper outer pack structure to facilitate attachment of the inner bag structure to the outer pack structure and provide for concurrent closure of both. 
     2. Description of the Prior Art 
     Soft pack structures such as backpacks, stuffsacks, rucksacks etc. are of course well known. The better quality of such packs are formed of wear resistant, woven material coated on one side therewith with a substantially water impervious material, typically a nylon or polyester cloth coated on one side with a urethane material to resist water penetration. In many instances, such packs are utilized to carry clothing, food stuffs, equipment etc. critical to the very survival of the user. Heretofore such pack structures have provided only limited resistance to moisture penetration under adverse conditions, i.e., rain, wet snow, water spray etc. While the materials from which the pack structures are constructed are in fact highly water resistant as a result of coatings such as the urethane coatings, the water resistant integrity of such structures is severely compromised by the many perforations in typical pack structures, i.e., for seams to form the pack structure itself, and to attach panels, bottoms, shoulder straps, pockets, holding loops, and various other sewn constructions and features. While the synthetic materials and water resistant coatings thereon are highly resistant to water penetration, such materials are not self healing around perforations. Thus water readily infiltrates through the many needle and other holes formed in the pack structure as an unavoidable result of conventional production of such pack structures. 
     To combat the serious threat of wetting of the contents of the pack structure, it has heretofore been the practice to wrap the separate, or entire, contents of the sack in individual waterproof enclosures, such as polymer film bags commonly employed as &#34;garbage&#34; bags. Such efforts, while inconvenient, are often effective. However, in the instance of film enclosures, during the course of an extended expedition, it is not unusual for the polymer film bags to become ripped and perforated. 
     It has also been customary to line certain pack bags with a second layer of material to decrease water penetration through the coated surfaces. However, this type of construction does not diminish total seams (and subsequent reduced needle hole water penetration) since the lining is simply a mirror image of the outer material layers and has identical seam placement and number as the outer material layer. 
     SUMMARY OF THE INVENTION 
     The present invention, which provides a heretofore unavailable improvement over soft previous pack structures with regard to protection of the contents thereof against water infiltration comprises a substantially conventional outer soft pack structure preferably including an opening defined therein and including means to close and cover the opening, preferably flap means to protect the opening from water, such as rain. In addition, a complementary inner bag structure of a water resistant material, i.e., a woven synthetic or other bag material coated on one side with a water proof coating, positioned within the outer bag structure, with the upper portion thereof cooperating with the closure means of the outer bag structure to both secure the inner bag structure therein and provide for concurrent opening and closure of both the inner and outer bag structures. Preferably the outer bag structure is coated with water resistant material on the inner surface thereof, and the inner bag structure is coated on the outer surface thereof to isolate water infiltrating the outer bag structure from the interior of the inner bag stucture. 
     Accordingly, an object of the present invention is to provide a new and improved soft bag structure which provides for convenient and reliable protection against water infiltration of the bag structure. 
     Another object of the present invention is to provide a new and improved soft bag structure which may be packed and used as conveniently as a conventional bag structure. 
     Yet another object of the present invention is to provide a new and improved soft bag structure which provides reliable protection against water infiltration over prolonged use. 
     Still another object of the present invention is to provide a new and improved soft bag structure which may be simply and economically produced and used. 
     Still yet another object of the present invention is to provide a new and improved soft bag structure which permits the simple and economical replacement of the inner bag structure when worn or wet. 
     These and other objects and features of the present invention will become apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a perspective, expanded view of a soft bag structure in accord with the instant invention illustrating the inner and outer bag structures in a removed relationship; and 
     FIG. 2 is a sectional view of a preferred interface between the inner and outer bag structures of FIG. 1 at the closure portions thereof. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various figures, a pack structure in accord with the instant invention is illustrated in FIG. 1 and generally designated by the reference numeral 10. Pack structure 10 includes an outer pack structure 12, which is of substantially conventional construction. Outer pack structure 12 is, as is conventional, formed of a fabric conventionally used to construct packs, i.e., a nylon cloth coated with a urethane water resistant coating. Such material is itself abrasion resistant and highly resistant to water penetration. However, as illustrated, outer pack structure 12 includes a number of seams, i.e., 14, 16 and 18, a number of straps 19 sewn thereto at, for instance, positions 20, accessory loops 21 sewn at positions 22 and exterior pocket 24 sewn at, for instance, positions 25. Other typical sewn attachments, not specifically illustrated, include shoulder straps 27, waist belt 28, cross harness, compression straps, ski pockets etc. These many structural features seriously compromise the water resistance of outer pack structure 12, and require a complicated and expensive component. 
     Outer pack structure 12 includes at the upper portion thereof an opening 29 defined therein and a plurality of spaced grommets 30 adapted to received a drawstring to close opening 29 at the upper portion of outer pack structure 12. Flap 33, in turn, is adapted to fit over the upper portion of outer bag structure 12, and be secured by mating buckles 35. Thus, as discussed heretofore, though outer pack stucture 12 is produced of essentially water proof material, the many seams and attachment points for accessory loops, compression straps, etc. require that the integrity of the structure be substantially compromised by many needle perforations with accompanying potential for water leakage. 
     Accordingly, a much simpler inner bag structure 40 is provided of a shape complementary to that of outer pack structure 12 and adapted to fit within outer pack structure 12. Inner bag structure 40 is preferably produced of a similar material to that of outer pack structure 12, and preferably the water proof coating on outer pack structure 12 is on the inner side thereof, and the waterproof coating of inner bag stucture 40 is on the outer surface thereof. Further, though inner bag structure 40 may include limited seams 42, such seams 42 are preferably positioned so as to be remote from seams 14, 16 and 18 of outer pack structure 12, or transverse to seam 18 of outer pack structure 12 as is seam 42, as well as spaced from portions of outer pack structure 12 having substantial sewn areas. Seams of outer pack structure 12 and inner bag structure 40 are functionally transverse when intersecting at angles between about 45° and 135°. In the example illustrated, grommets 45 are provided at the upper portion of inner bag structure 40 and spaced in a manner complimentary to grommets 30 provided through the upper portion of outer pack structure 12. 
     With reference to FIG. 2, it will be seen that a draw cord 50 may be positioned through adjacent grommets 30 and 45. Accordingly, outer pack structure 12 will be aligned with adjacent inner bag structure 40 and secured thereto by drawstring 50. In this simple manner, inner bag structure 40 may be easily and securely positioned within outer pack structure 12, closed concurrently with outer pack structure 12 by pulling on drawstring 50, but easily removeable from outer pack structure 12 for replacement or airing and drying, as well as inconspicuous in normal use. The waterproof interface between the adjacent surfaces of outer pack structure 12 and inner bag structure 40 substantially preclude infiltration of water to the interior of inner bag structure 40. What water passes through the many needle holes in outer pack structure 12 merely collects on the substantially unbroken outer waterproof surface of inner bag structure 40, and tends to be contained at the interface therebetween. Even when used for extensive periods of time, little detrimental wear will occur to the protected waterproof surfaces, thus providing reliability of bag structure 10. However, should wear occur, the simple and economical inner bag structure 40 may be easily replaced. 
     In summary, the instant invention addresses the long standing problem of protecting the contents of a soft pack structure which, though of waterproof material, necessarily includes a great many needle or other perforations as a result of construction of the pack. A simple, lightweight inner bag is provided in such a manner that it functions integrally with the outer pack while providing great integrity against water infiltration. While a particularly preferred securing means between the inner and outer bag structures is disclosed, i.e., an interlaced drawstring for simple attachment and closure of the pack and bag structure, it will be appreciated that other attachment means, including releasable fasteners, Velcro etc. may be employed between the upper portions of the two structures. Thus by attachment of the inner bag structure adjacent the outer pack structure opening, concurrent opening and closing of the two structures will result. While of particular utility with various backpacks, the concept may be employed with other soft bags including stuff sacks. Since the simple inner bag requires few seams and provides the better barrier against water, a worn pack can be largely rejuvenated against water leakage by the simple and economical replacement of the inner bag structure. 
     Although only several embodiments of the present invention have been illustrated and described, it is anticipated that various changes and modifications will be apparent to those skilled in the art, and that such changes may be made without departing from the scope of the invention as defined by the following claims.