Abstract:
A garment worn by a wearer has an exterior shell and an interior shell with various impact absorbing material between the exterior shell and the interior shell. The impact absorbing material includes multiple structures, such as rods or filaments, capable of deforming when force is applied then returning to its state prior to application of the force. In various embodiments, the impact absorbing material is manufactured using injection molding to allow positioning of various structures in the impact absorbing material relative to each other during manufacture. During manufacturing, one or more living hinges are included in portions of the impact absorbing material to allow certain portions of the impact absorbing material to be accurately positioned relative to each other. Other manufacturing methods may be used, such as three-dimensional printing may be used to include structures in the impact absorbing material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/276,791, filed on Jan. 8, 2016, which is hereby incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    A helmet protects a skull of the wearer from collisions with the ground, equipment, and other players. Present helmets were designed with the primary goal of preventing traumatic skull fractures and other blunt trauma. In general, a helmet includes a hard, rounded shell and cushioning inside the shell. When another object collides with the helmet, the rounded shape deflects at least some of the force tangentially while the hard shell distributes the normal force over a wider area of the head. Such helmets have been successful at preventing skull fractures but leave the wearer vulnerable to concussions. 
         [0003]    A concussion occurs when the skull changes velocity rapidly relative to the enclosed brain and cerebrospinal fluid. The resulting collision between the brain and the skull results in a brain injury with neurological symptoms such as memory loss. Although the cerebrospinal fluid cushions the brain from small forces, the fluid does not absorb all the energy from collisions that arise in sports such as football, hockey, skiing, and biking. Helmets include cushioning to dissipate some of the energy absorbed by the hard shell, but the cushioning is insufficient to prevent concussions from violent collisions or from the cumulative effects of many lower velocity collisions. 
       SUMMARY 
       [0004]    In various embodiments, a helmet includes two generally concentric shells with impact absorbing structures between the shells. The inner shell may be somewhat rigid to protect against skull fracture and the outer shell may also somewhat rigid to spread impact forces over a wider area of the impact absorbing structures positioned inside the outer shell, or the outer shell may be more flexible such that impact forces locally deform the outer shell to transmit forces to a smaller, more localized section of the impact absorbing structures positioned inside the outer shell. The impact absorbing structures are secured between the generally concentric shells and have sufficient strength to resist forces from mild collisions. However, the impact absorbing structures undergo deformation (e.g., buckling) when subjected to forces from a sufficiently strong impact force. As a result of the deformation, the impact absorbing structures reduce energy transmitted from the outer shell to the inner shell, thereby reducing forces on the wearer&#39;s skull and brain. The impact absorbing structures may also allow the outer shell to move independently of the inner shell in a variety of planes or directions. Thus, impact absorbing structures reduce the incidence and severity of concussions as a result of sports and other activities. When the outer and inner shell move independently from one another, rotational acceleration, which contributes to concussions, may also be reduced. 
         [0005]    The helmet may include modular rows to facilitate manufacturing. A modular row includes an inner surface, an outer surface, and impact absorbing structures between the inner and outer surfaces. A modular row is relatively thin and flat compared to the assembled helmet, which reduces the complexity of forming the impact absorbing structures between the modular row&#39;s inner and outer surfaces. For example, the modular rows may be formed by injection molding, fusible core injection molding, or a lost wax process. When assembled, the inner surfaces of the modular rows may form part of the inner shell, and the outer surfaces of the modular rows may form part of the outer shell. Alternatively or additionally, the modular rows may be assembled between an innermost shell and an outermost shell that laterally secure the modular rows and radially contain them. In addition, adjacent rows may be laterally secured to each other. 
         [0006]    The impact absorbing material may be manufactured using injection molding to facilitate positioning of various structures in the impact absorbing material relative to each other during manufacture (e.g., a stand-off). The benefit of manufacturing the impact absorbing material in rows is to allow the structure to be injection molded, which greatly reduces manufacturing complexity and cost. During manufacturing, one or more living hinges may be included in portions of the impact absorbing material to allow certain portions of the impact absorbing material to be accurately positioned relative to each other. Other manufacturing methods may be used to include structures in the impact absorbing material, such as three-dimensional printing, fusible core injection molding, or lost wax casting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of an assembly of impact absorbing structures formed from modular rows, in accordance with an embodiment. 
           [0008]      FIG. 2  is a perspective view of a modular row, in accordance with an embodiment. 
           [0009]      FIG. 3  is a perspective view of a modular row, in accordance with an embodiment. 
           [0010]      FIGS. 4A and 4B  are cross-sectional views of an example process for manufacturing an impact absorbing member, in accordance with an embodiment. 
           [0011]      FIGS. 5A-5G  are cross-sectional views of impact absorbing members, in accordance with various embodiments. 
           [0012]      FIGS. 6A-6H  are cross-sectional views of impact absorbing members arranged in a modular row, in accordance with various embodiments. 
           [0013]      FIG. 7A  is a front view of a core for manufacturing an impact absorbing member, in accordance with an embodiment. 
           [0014]      FIG. 7B  is a side view of a core for manufacturing an impact absorbing member, in accordance with an embodiment. 
           [0015]      FIG. 7C  is a transparent top view of a core for manufacturing an impact absorbing member, in accordance with an embodiment. 
           [0016]      FIG. 7D  is a transparent angled view of a core for manufacturing an impact absorbing member, in accordance with an embodiment. 
           [0017]      FIG. 8A  is a transparent isometric view of a mold for manufacturing an impact absorbing member, in accordance with an embodiment. 
           [0018]      FIG. 8B  is a transparent isometric view of a side of a mold for manufacturing an impact absorbing member, in accordance with an embodiment. 
           [0019]      FIG. 8C  is a transparent isometric view of an opposing side of a mold for manufacturing an impact absorbing member, in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     Modular Helmet 
       [0020]      FIG. 1  is a perspective view of an assembly  100  of impact absorbing structures formed from modular rows  110 ,  120 , and  130 , in accordance with an embodiment. In general, a modular row includes an inner surface, an outer surface, and impact absorbing structures between the inner surface and the outer surface. The modular row may further include a protective layer (e.g., foam) less rigid than the impact absorbing structures that encloses a remaining volume between the inner surface and outer surface after formation of the impact absorbing members. When a helmet including the assembly  100  is worn, the inner surface is closer to the user&#39;s skull than the outer surface. Optionally, the modular row includes end surfaces connecting the short edges of the inner surface to the short edges of the outer surface. The inner surface, outer surface, and end surfaces form a slice with two parallel flat sides and an arc or bow shape on two other opposing sides. The end surfaces may be parallel to each other or angled relative to each other. The modular rows include one or more base modular rows  110 , crown modular rows  120 , and rear modular rows  130 . The assembly  100  may include further shells, such as an innermost shell, an outermost shell, or both, that secure the modular rows relative to each other and capture the structure between the innermost and outermost shells when assembled for durability and impact resistance. 
         [0021]    The base modular row  110  encircles the wearer&#39;s skull at approximately the same vertical level as the user&#39;s brow. The crown modular rows  120  are stacked horizontally on top of the base modular row  110  so that the long edges of the inner and outer surfaces form parallel vertical planes. The end surfaces of the crown modular rows  120  rest on a top plane of the base modular row. The outer surfaces of the crown modular rows  120  converge with the outer surface of the base modular row  110  to form a rounded outer shell. Likewise, the inner surfaces of the crown modular rows  120  converge with the inner surface of the base modular row  110  to form a rounded inner shell. Thus, the crown modular rows  120  and base modular row  110  form concentric inner and outer shells protecting the wearer&#39;s upper head. The outer surface of a crown modular row  120  may form a ridge  122  raised relative to the rest of the outer surface. The ridge  122  may improve resistance to impact forces or facilitate a connection between two halves (e.g., left and right halves) of an outermost layer of a helmet including the assembly  100 . 
         [0022]    The rear modular rows  130  are stacked vertically under a rear portion of the base modular row  110  so that the long edges of the inner and outer surfaces form parallel horizontal planes. The inner surface of the topmost rear modular row  130  forms a seam with the inner surface of the base modular row  110 , and the outer surface of the topmost rear modular row  130  forms a seam with the outer surface of the base modular row  110 . Thus, the rear modular rows  130  and the rear portion of the base modular row  110  form concentric inner and outer shells protecting the wearer&#39;s rear lower head and upper neck. 
       Modular Row 
       [0023]      FIG. 2  is a perspective view of a base modular row  110 , in accordance with an embodiment. The base modular row  110  includes two concentric surfaces  103  (e.g., an inner surface and an outer surface), end surfaces, and impact absorbing structures  105 . 
         [0024]    As illustrated, the impact absorbing structures  105  are columnar impact absorbing members mechanically secured to both concentric surfaces  103 . An end of the impact absorbing structure  105  may be mechanically secured to a concentric surface  103  as a result of integral formation, by a fastener, by an adhesive, by an interlocking end portion (e.g., a press fit), another technique, or a combination thereof. An end of the impact absorbing member is secured perpendicularly to the local plane of the concentric surface  103  in order to maximize resistance to normal force. However, one or more of the impact absorbing members may be secured at another angle to modify the resistance to normal force or to improve resistance to torque due to friction between an object and the outermost surface of a helmet including assembly  100 . The critical force that buckles the impact absorbing member increases with the diameter of the impact absorbing member and decreases with the length of the impact absorbing member. 
         [0025]    Generally, an impact absorbing member has a circular cross section to eliminate stress concentration along edges, but other cross-sectional shapes (e.g., squares, hexagons) may be used to simplify manufacturing or modify performance characteristics. Generally, an impact absorbing structure is formed from a compliant yet strong material such as an elastomeric substrate such as hard durometer plastic (e.g., polyurethane, silicone) and may include a core of a softer material such as open or closed-cell foam (e.g., polyurethane, polystyrene) or fluid (e.g., air). After forming the impact absorbing members, a remaining volume between the concentric surfaces  103  (that is not filled by the impact absorbing members) may be filled with foam, fluid, or another material less rigid than the impact absorbing members. 
         [0026]    The concentric surfaces  103  are curved to form an overall rounded shape (e.g., spherical, ellipsoidal) when assembled into a helmet shape. The concentric surfaces  103  and end surfaces  104  may be formed from a material that has properties stiffer than the impact absorbing members such as hard plastic, foam, metal, or a combination thereof, or formed from the same material as the impact absorbing members. To facilitate manufacturing of the base modular row  110 , a living hinge technique may be used. The base modular row  110  may be manufactured as an initially flat modular row, where the long edges of the concentric surfaces  103  form two parallel planes. For example, the base modular row  110  is formed by injection molding the concentric surfaces  103 , the end surfaces  104 , and the impact absorbing structures  105 . The base modular row  110  may then be bent to form hinge. The living hinge may be created by injection molding a thin section of plastic between adjacent structures or rows. The plastic is injected into the mold such that the plastic fills the mold by crossing the hinge in a direction transverse to the axis of the hinge, thereby forming polymer strands perpendicular to the hinge, thereby creating a hinge that is robust to cracking or degradation. 
         [0027]      FIG. 3  is a perspective view of a modular row  110 , in accordance with an embodiment. The modular row  110  has a beveled edge with a cross-section that tapers from a base to an edge along which the impact absorbing members  105  are secured. For example, the modular row  110  has a pentagonal cross section where the impact absorbing members  105  are mechanically secured along an edge formed opposite the base of the pentagonal cross-section. The pentagon has two perpendicular sides extending away from the base of the pentagon to two sides that converge at an edge to which the impact absorbing members  105  are secured. As another example, the modular row  110  has a triangular cross section (e.g., isosceles triangle), and the impact absorbing members  105  are secured along an edge opposite the base of the triangular cross-section. Relative to a rectangular cross-section, the tapered cross-section reduces the mass to secure the impact absorbing members  105  to the base of the modular row  110 . The base of the modular row  110  is generally wider than an impact absorbing member  105  in order to form a shell when assembled with adjacent modular rows  110 . The general benefit of forming the base of the rows in this manner is to increase moldability of these structures. 
       Manufacturing Impact Absorbing Members 
       [0028]      FIGS. 4A and 4B  are cross-sectional views of an example process for manufacturing an impact absorbing member  105 , in accordance with an embodiment.  FIG. 4A  illustrates a partially formed modular row  110 A including a concentric surface  103 A and impact absorbing members  105 A formed through a standard injection molding, fusible core injection molding, or last wax casting process. Cores corresponding to an interior of the impact absorbing members  105  are formed (e.g., by molding or casting) from a core material (e.g., wax, chocolate, salt, soap, glycerine, tin-bismuth alloy, polyvinyl acrylate (PVA) support material). The cores are then held inside an injection mold to form hollow portions inside the impact absorbing members  105 A. The injection molding forms the concentric surface  103 A and the hollow columns of the impact absorbing members  105  around the cores. For example, the injection molding is performed by injecting a plastic (e.g., urethane) between upper and lower pieces of the injection mold. The cores are then removed from the impact absorbing members  105 A using a process such as heating the core above the melting point of the core (e.g., wax) and below the melting point of the rigid plastic. As another example, the core is dissolved in a solvent that does not harm the structural integrity of the rigid plastic. As a result, the impact absorbing members  105  become hollow tubes secured on a planar or rounded concentric surface  103 A. 
         [0029]      FIG. 4B  illustrates a modular row  110  including two concentric surfaces  103 B and  103 C as well as impact absorbing members  105 B formed by combining foam with the partially formed modular row  110 A. The foam forms the concentric surface  103 B and augments the plastic of concentric surface  103 A to form concentric surface  103 C. For example, the foam is injected between two pieces of an injection mold. Thus, the injection molding process forms impact absorbing members  105  including a plastic shell filled with foam. The plastic increases a yield strength of the impact absorbing members  105  and increases the energy dispersed by deformation of the impact absorbing members. The foam further dissipates energy from collisions and increases a yield strength of the impact absorbing members  105  relative to a hollow cylindrical rigid plastic shell. 
         [0030]    Although illustrated as being planar, the concentric surfaces  103  may be rounded, as illustrated in  FIGS. 1 and 2 . Further, the injection molding may be used to form impact absorbing members  105  between an inner and outer shell. However, multiple rows of impact absorbing members cannot be simultaneously manufactured via a traditional split mold injection molding process. If the injection molding process added a middle mold piece between first and second rows of impact absorbing members, the middle mold piece could not be removed without being broken down into small sections that could be maneuvered between the formed impact absorbing members  105 . Thus, simultaneously forming multiple rows of impact absorbing members would require a complex molding process with an injection mold having more than two pieces, some of which would not be reusable. In contrast, a modular row  110  may be formed using an injection mold having only two halves, thereby simplifying the manufacturing process. The modular rows  110  are then assembled into a structure having multiple rows of impact absorbing members  105  distributed between two concentric shells. 
         [0031]    As an alternative to using injection molding, the modular rows  110  may be formed through three-dimensional (3D) printing. For example, a 3D printer extrudes plastic to form layers of a lower concentric surface, then the impact absorbing members, and then an upper concentric surface. Example materials used in 3D printing include thermoplastics for fused filament fabrication, but other 3D printing materials and techniques may be used as well. The 3D printing process may be used to form the structure illustrated in  FIG. 4A , and then another process (e.g., injection molding process with foam) may be used to form the structure in  FIG. 4B . Alternatively, the 3D printing process may be used to form an entire modular row  110  from one or more materials or an entire matrix of impact absorbing structures in once piece. 
       Securing Impact Absorbing Members in Modular Row 
       [0032]      FIGS. 5A-5G  are cross-sectional views of impact absorbing members  105 , in accordance with various embodiments. The impact absorbing members  105  may be mechanically secured at both ends to the concentric surfaces  103 A and  103 B using various techniques. The illustrated techniques may be used in any combination to secure one or both ends of the impact absorbing members  105  to concentric surfaces. 
         [0033]    In  FIGS. 5A and 5B , the surface  103 A includes a protrusion  505 , which may have a circular, square, or other shape. The impact absorbing member  105  forms a hole that accommodates the shape of the protrusion  505 . In  FIG. 5B , the surface  103 A includes protrusion  505 , and impact absorbing member  105  forms a hole  510  that accommodates the protrusion  505 . The hole  510  may be filled with foam or may be hollow. For example, the hole  510  results from manufacturing the impact absorbing member  105  as a hollow cylindrical shell. Thus, the protrusion  505  interlocks with the hole to laterally secure the impact absorbing member  105 . The protrusion  505  may also be adhesively bonded, heat welded, heat staked, or vibration welded into the hole  510 . 
         [0034]    In  FIG. 5C , the surface  103 A forms a hole  515  that accommodates the shape of the protrusion  505 . For example, the hole  515  is a cylindrical cavity to accommodate the cylindrical impact absorbing member  105 . The impact absorbing member  105  may be press fit with the hole  515  to restrict the lateral and axial movement of the impact absorbing member  105 . Alternatively, the clearance between the impact absorbing member  105  and the hole  515  may be greater than in a press fit but sufficiently small to laterally secure the impact absorbing member  105 . The end of the impact absorbing member  105  may also be adhesively bonded, heat welded, heat staked, or vibration welded into the hole  515 . In  FIG. 5D , the surface  103 A still forms a hole  515 , but the impact absorbing member  105  further includes an end cap  520  having a greater cross-sectional area than the middle portion of the impact absorbing member  105 . The hole and end cap  520  laterally secure the impact absorbing member (and may axially secure the impact absorbing member in a press fit). The end cap  520  beneficially increases a contact area between the surface  103 A and the impact absorbing member  105 . The end cap  520  may be a separate piece or integrally formed with the impact absorbing member  105 . In the latter case, the end cap  520  may be forced into the hole, causing a transient deformation after which the end cap  520  would recover its shape due to its elastomeric properties. 
         [0035]    In  FIG. 5E , the surface  103 A includes collar  525 . The collar  525  may completely encircle an end of the impact absorbing member  105  or may include one or more opposing pairs of arcs to secure opposite sides of the impact absorbing member  105 . Relative to a protrusion  505 , the collar  525  increases an area of contact between the impact absorbing member  105  and the surface  103 A, so the collar  525  beneficially improves resistance to lateral forces. The impact absorbing member  105  may also be adhesively bonded, heat welded, heat staked, or vibration welded into the collar  525 .  FIGS. 5A-E  illustrate the impact absorbing member  105  as being formed integrally with the surface  103 B. Alternatively, the impact absorbing member  105  is formed separately from the surfaces  103 A and  103 B and mechanically secured at both ends by the above-described structures, adhesives, layered materials, fasteners, or a combination thereof. 
         [0036]    In  FIG. 5F , the surfaces  103 A, a lower layer of surface  103 B, and a core of the impact absorbing member  105  are formed integrally from material  535 , and an upper layer of surface  103 B is integrally formed with an outer shell of the impact absorbing member  105  from material  530 . For example, the process described with respect to  FIGS. 4A and 4B  may be employed, where material  530  is a plastic and material  535  is foam. By forming the connections between the impact absorbing member  105  and the surfaces  103 A and  103 B integrally, the process obviates a dedicated structure to laterally and axially secure the impact absorbing member relative to the surfaces  103 A and  103 B. 
         [0037]    In  FIG. 5G , the surfaces  103 A and  103 B are integrally formed with upper and lower portions  540  of the impact absorbing member  105 . A collar  545  encircles a seam between the upper and lower portions  540  to laterally secure the upper and lower portions. For example, the collar  545  is formed from foam or rubber. Alternatively or additionally to the collar  545 , one of the portions  540  includes a protrusion (such as protrusion  505 ) and the other portion  540  forms a hole to accommodate the protrusion. The protrusion may also be adhesively bonded, heat welded, heat staked, or vibration welded into the hole. 
       Layout of Impact Absorbing Members in Modular Row 
       [0038]      FIGS. 6A-6H  are cross-sectional views of impact absorbing members  105  arranged in a modular row  110 , in accordance with various embodiments. As illustrated, the impact absorbing members  105  and modular row  110  may be formed through an injection molding process between a first piece of a mold above the modular row  110  and a second piece of the mold below the modular row  110 . For example, the separation line  605  illustrates a contact surface between upper and lower pieces of the injection mold. Having no vertically stacked impact absorbing members  105  enables using a mold having only upper and lower pieces, which can be easily separated from the part by pulling them away from the part. If multiple impact absorbing members  105  were vertically stacked, the upper and lower pieces of the mold could not form the inward-facing contours of the impact absorbing members without using internal mold pieces, cores, or other inserts that would increase manufacturing complexity and cost. Removing internal mold pieces would add an additional manufacturing step, and it would be difficult to form reusable internal mold pieces. Thus, the illustrated arrangements ensure compatibility with an injection mold having only two pieces. 
         [0039]    In  FIG. 6A , the impact absorbing members  105  are arranged in a line. However, this arrangement may increase stress along those portions of the surface  103  vertically farthest from the impact absorbing members  105 , particularly along the long edges of the modular rows  110 . By spacing the impact absorbing members  105  across two or more vertical levels (as in  FIGS. 6B-6H ), stresses are distributed more evenly along the illustrated vertical dimension. The illustrated arrangements generally include a horizontally repeated spatial pattern of the impact absorbing members  105 , which beneficially improves horizontal distribution of stress. The impact absorbing members  105  are connected by a single path traced by the separation line  605 , which illustrates where upper and lower pieces of an injection mold meet to form the surfaces  103  and impact absorbing members  105  of the modular row  110 . Because none of the impact absorbing members  105  overlap vertically, the modular row  110  may be formed in an injection mold having only two pieces. The impact absorbing members  105  may be horizontally spaces to provide at least two to three degrees of shut-off between vertical rows. 
         [0040]      FIG. 7A  is a front view of an embodiment of a core  700  for manufacturing one or more impact absorbing members  705 . The core  700  corresponds to the cavity from which the impact absorbing members  705  will be formed (e.g., by molding or casting) from a material (e.g., wax, chocolate, salt, soap, glycerine, tin-bismuth alloy, polyvinyl acrylate (PVA) support material), as further described above in conjunction with  FIGS. 4A and 4B . The core  700  also includes portions corresponding to a concentric surface  710 A and another concentric surface  710 B, so when the core  700  is held between a side and an opposing side of a mold, injection molding forms the concentric surface  710 A and the other concentric surface  710 B, as well as hollow columnar structures around the interiors of the impact absorbing members  705  that comprise portions of the core  700 . 
         [0041]      FIG. 7B  is a side view of the core  700  for manufacturing one or more impact absorbing members  705  shown in  FIG. 7A . In  FIG. 7B , a parting line  715  is shown on the portions of the core  700  corresponding to the interior of various impact absorbing members  705 . The parting line  715  indicates a position on the core  700  where the side of the mold contacts the the opposing side of the mold when the core  700  is held within the mold. To facilitate removal of the mold from the core  700  after forming the concentric surface  710 A and the other concentric surface  710 B, as well as hollow columnar structures around the interiors of the impact absorbing members  705 , the core  700  is tapered by a particular amount proximate to the parting line  715 , the amount of taper (also referred to as draft) allows the mold to be more easily released after the concentric surface  710 A and the other concentric surface  710 B, as well as hollow columnar structures around the interiors of the impact absorbing members  705  are formed. The core  700  is tapered along a plane perpendicular to a plane including the parting line  715 . 
         [0042]      FIG. 7C  is a transparent top view of the core  700  for manufacturing an impact absorbing member also shown in  FIGS. 7A and 7B . The parting line  715 , indicating a location on the core  700  where the side and the opposing side of the mold contact each other when the core is placed in the mold is identified in  FIG. 7C .  FIG. 7D  is a transparent angled view of the core  700  shown in  FIG. 7A . As shown in  FIG. 7D , the portion of the core corresponding to a concentric surface  710  is tapered by a particular amount (also referred to as draft) to allow the mold to be more easily released after the concentric surface  710 A and the other concentric surface  710 B, as well as hollow columnar structures around the interiors of the impact absorbing members  705  are formed. The portion of the core  700  corresponding to the concentric surface  710  is tapered in a direction perpendicular to a plane including the portion of the mold contacting the portion of the core  700  corresponding to the concentric surface  710 , 
         [0043]    To form the impact absorbing member using the core  700 , the core  700  is held between a side and an opposing side of a mold, injection molding forms the concentric surface  710 A and the other concentric surface  710 B, as well as hollow columnar structures around the interiors of the impact absorbing members  705  that comprise portions of the core  700 .  FIG. 8A  is a transparent isometric view of one embodiment of a mold  800  for manufacturing an impact absorbing member. As shown in  FIG. 8A , the mold  800  includes a side  805  and an opposing side  810 . The mold  800  holds the core  700  between the side  805  and the opposing side  810  so the side  805  contacts the opposing side  810  at a portion of the core  700  identified by the parting line  715  in  FIGS. 7B and 7C .  FIG. 8B  is a transparent isometric view of a side  805  of the mold  800  shown in  FIG. 8A , while  FIG. 8C  is a transparent isometric view of the opposing side  810  of the mold  800  shown in  FIG. 8A . As further described above in conjunction with  FIGS. 4A and 4B , in various embodiments a plastic (e.g., urethane) is injected between the side  805  and the opposing side  810  of the mold  800  while the core  700  is secured between the side  805  and the opposing side  810 . The core  700  is subsequently removed from the resulting plastic structure to form impact absorbing members; for example; the core  700  is heated to a temperature above a melting point of a material comprising the core  700  (e.g., wax) and below the melting point of the plastic. As another example, the core  700  is dissolved in a solvent that does not harm the structural integrity of the plastic. Hence, the resulting impact absorbing members are hollow tubes secured on a planar or rounded concentric surface. 
         [0044]    Although described throughout with respect to a helmet, the impact absorbing structures and manufacturing techniques described herein may be applied with other garments such as padding, braces, and protectors for various joints and bones. 
       Additional Configuration Considerations 
       [0045]    The foregoing description of the embodiments of the disclosure has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. 
         [0046]    The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosed embodiments are intended to be illustrative, but not limiting, of the scope of the disclosure.