1. A fold-flat personal respiratory device comprising:
- a generally planar central panel including a layer of filter media and having opposing first and second side edges and first and second end edges;
- a first side panel joined to said central panel along said first side edge;
- a second side panel joined to said central panel along said second side edge; the device being manually configurable from a folded configuration in which said side panels are substantially parallel to a planar surface of said central panel and an operational configuration in which said central and first and second side panels form a cup-shaped respiratory chamber;
the device further comprising a rigid or semi-rigid endoskeleton member mounted along a planar surface of said central panel and extending between said first and second side edges and/or said first and second end edges.
2. A fold-flat respiratory device according to claim 1, wherein said endoskeleton member is formed of semi-rigid plastics material.
3. A fold-flat respiratory device according to claim 1 or claim 2, wherein said endoskeleton member comprises first and second elongate longitudinal arm portions that extend from a central region of the central panel to a position at or adjacent to respective end edges thereof.
4. A fold-flat respiratory device according to any of the preceding claims, wherein said endoskeleton member comprises first and second transverse arm portions that extend from a central region of the central panel to respective side edges thereof.
5. A fold-flat respiratory device according to claim 3 or claim 4, wherein said first and second elongate longitudinal arm portions each comprise a generally

triangular frame member comprising a pair of arms spaced apart at said central region and meeting at an apex at or adjacent to a respective end edge.
6. A fold-flat respiratory device according to claim 5, wherein said apex is rounded.
7. A fold-flat respiratory device according to any of claims 4 to 6, wherein said first and second transverse arm portions each comprise a generally square or rectangular frame member having a pair of substantially parallel, spaced-apart end arms and a distal side arm extending therebetween, said end arms extending transversely from said central region such that said side arm is at, or adjacent to, and substantially parallel to, a respective side edge of said central panel.
8. A fold-flat respiratory mask according to any of claims 3 to 7, wherein said endoskeleton member further comprises a central frame portion comprising a generally square or rectangular frame member, located at said central region of said central panel, and from which said first and second elongate longitudinal arm portions and/or said first and second transverse arm portions extend.
9. A fold-flat respiratory device according to any of the preceding claims, further comprising an exhalation valve assembly mounted within said endoskeleton member, at a substantially central region of said central panel.
10. A fold-flat respiratory device according to claim 9 when dependent on claim 8, wherein said central frame portion includes a generally cylindrical frame member mounted or integrated in said central frame portion and configured to receive an exhalation valve assembly.

11 .A fold-flat respiratory device according to claim 8, wherein said central frame portion of said endoskeleton member is provided with a reinforcing member that extends between a pair of opposing side edges thereof.
12. A fold-flat respiratory device according to claim 11, wherein said reinforcing member comprises a pair of reinforcing arms, each extending between a respective pair of opposing side edges and intersecting at a generally central location within the central frame portion.
13. A method of manufacturing a fold-flat respiratory device according to any of the preceding claims, comprising: providing an integrated template comprising said central panel and said first and second side panels; and mounting or adhering said endoskeleton member onto a planar surface of said central panel such that it extends between said first and second end edges and/or said first and second side edges thereof.
14. A method according to claim 13, wherein said central panel comprises a generally square or rectangular central region defining said first and second opposing side edges and a pair of respective end portions extending from said central region, each end portion having tapered opposing side edges and terminating at a respective end edge of said central panel, each side panel being integrally joined to said central panel along a respective side edge thereof and having a pair of tapered end portions, the method further comprising joining, at adjacent edges thereof, respective end portions of said central panel and said side panels to form said cup-shaped respiratory chamber.
15. A method according to claim 13 or claim 14, wherein said endoskeleton member comprises an exhalation valve frame member and the central panel

includes a generally central opening, the method further comprising mounting an exhalation valve assembly in said exhalation valve frame member such that it is located within said opening. 16. A method according to any of claims 13 to 15, further comprising joining one or more straps to said central panel, at or adjacent respective end edges thereof.