Porous composite article

1. A porous composite comprising:

(a) porous membrane having a structure defining a plurality of pores extending therethrough,

(b) nonporous discontinuous surface layer affixed to said porous membrane, said nonporous discontinuous surface layer having a thickness of less than 5 μm and having rents, wherein the rents form regions of gas permeability, and

(c) a coating disposed upon wherein at least a portion of the porous composite is rendered oleophobic.

2. The porous composite of claim 1 wherein the said porous membrane comprises expanded PTFE.

3. The porous composite of claim 1 wherein the said microporous membrane comprises UHMWPE.

4. The porous composite of claim 1 wherein the said nonporous discontinuous surface layer comprises thermoplastic.

5. The porous composite of claim 1 wherein the said nonporous discontinuous surface layer comprises fluoroplastic.

6. The porous composite of claim 1 wherein the said nonporous discontinuous surface layer comprises FEP.

7. The porous composite of claim 1 wherein said porous composite has an oil rating of greater than about 2.

8. The porous composite of claim 1 wherein the said porous composite is laminated to a support layer.

9. The porous composite of claim 8 wherein the said support layer comprises a nonwoven.

10. The porous composite of claim 8 wherein the said support layer comprises an expanded PTFE membrane.

11. A venting apparatus having an opening therein for venting an enclosure and for preventing passage of a liquid, said venting apparatus comprising a porous composite venting element forming a gas-permeable barrier to said liquid, said porous composite venting element comprising:

a) porous membrane having a structure defining a plurality of pores extending therethrough, and

b) nonporous discontinuous surface layer affixed to said porous membrane, said nonporous discontinuous surface layer having a thickness of less than 5 μm and having rents, whereby the nonporous discontinuous surface layer comprises regions of gas permeability corresponding to the rents.

12. The venting apparatus of claim 11 in which the venting element has a liquid exposure side oriented towards the liquid, the liquid exposure side comprising said nonporous discontinuous surface layer.

13. The venting apparatus of claim 11 in which the porous composite venting element has a interior face and an exterior face and wherein the interior face and the exterior face comprise said nonporous discontinuous surface layer.

14. The venting apparatus of claim 11 wherein the said porous membrane comprises expanded PTFE.

15. The venting apparatus of claim 11 wherein the said porous membrane comprises UHMWPE.

16. The venting apparatus of claim 11 wherein the said nonporous discontinuous surface layer comprises thermoplastic.

17. The venting apparatus of claim 11 wherein the said nonporous discontinuous surface layer comprises fluoroplastic.

18. The venting apparatus of claim 11 wherein the said nonporous discontinuous surface layer comprises FEP.

19. The venting apparatus of claim 11 wherein the said porous composite has an oil rating greater than about 2.

20. The venting apparatus of claim 11 wherein the said porous composite is laminated to a support layer.

21. A venting apparatus having an opening therein for venting an enclosure and for preventing passage of a liquid, said venting apparatus comprising:

porous composite venting element forming a gas-permeable barrier to said liquid, said porous composite venting element comprising:

a) porous membrane having a structure defining a plurality of pores, extending therethrough,

b) nonporous discontinuous surface coating said porous membrane, said nonporous discontinuous surface coating having a thickness of less than 5 μm and blocking at least some of the pores, whereby the porous composite surface has regions of gas permeability and gas impermeability.

22. The porous composite of claim 21 wherein the said nonporous discontinuous surface layer comprises thermoplastic.

23. The porous composite of claim 21 wherein the said nonporous discontinuous surface layer comprises fluoroplastic.

24. The porous composite of claim 21 wherein the said nonporous discontinuous surface layer comprises FEP.

25. A venting apparatus having an opening therein for venting an enclosure, said enclosure defining an internal space and an external space, said venting apparatus preventing passage of a liquid between the internal space and the external space, the venting apparatus comprising:

a porous composite venting element forming a liquid-tight, gas-permeable seal of said opening, said porous composite venting element having a liquid face adjacent to the liquid, the porous composite venting element comprising:

a) porous membrane having a structure defining a plurality of pores extending therethrough,

b) nonporous discontinuous surface covering at least a portion of the liquid face of said porous membrane, said nonporous discontinuous surface having a thickness of less than 5 μm and blocking at least some of the pores and having openings therein, and

whereby the surface of said porous composite has regions of gas permeability and regions of gas impermeability.

26. The venting apparatus of claim 25 wherein the said microporous composite venting element further comprises an oleophobic coating.

27. The venting apparatus of claim 25 wherein said microporous membrane layer is expanded PTFE.

28. The venting apparatus of claim 25 wherein said microporous membrane layer is UHMWPE.

29. The venting apparatus of claim 25 wherein said nonporous discontinuous surface layer comprises thermoplastic.

30. The venting apparatus of claim 25 wherein said nonporous discontinuous surface layer comprises fluoropolymer.

31. The venting apparatus of claim 25 wherein said nonporous discontinuous surface layer comprises FEP.

32. The venting apparatus of claim 25 wherein the said porous composite surface has regions of gas permeability and regions of gas impermeability and wherein the area ratio of gas permeability to gas impermeability is no greater than 0.2:1.