permeable

from WordNet (r) 3.0 (2006)

permeable
    adj 1: allowing fluids or gases to pass or diffuse through;
           "permeable membranes"; "rock that is permeable by water"
           [ant: {impermeable}]

from The Collaborative International Dictionary of English v.0.48

Permeable \Per"me*a*ble\, a. [L. permeabilis: cf. F.
   perm['e]able. See {Permeate}.]
   Capable of being permeated, or passed through; yielding
   passage; passable; penetrable; -- used especially of
   substances which allow the passage of fluids; as, wood is
   permeable to oil; glass is permeable to light. --I. Taylor.
   [1913 Webster]