Wiktionary
a. permeable to some things and not to others, as a cell membrane which allow through some molecules through but blocks other substances.
WordNet
adj. (of a membrane) selectively permeable
Wikipedia
Usage examples of "semipermeable".
Living and growing pancreatic cells are encapsulated in a coiled tube of semipermeable membrane, a co-polymer of polyvinyl chloride and poly acrylonitrile.
Forgetting the tie-downs until he saw the elastic bands rip free and fly into space, Daeman lifted the sonie ten feet above the metal terrace, twitched the stick, fed power to the rear thrusters, went off course, quickly realigned before smashing into metal instead of window, and hit the semipermeable square doing thirty or forty miles per hour.
He adjusted it for transparent and semipermeable, and then turned the wheel on the seal lock of the door leading to the back of the payload section.
Daeman had watched Harman burst through the semipermeable membrane and fall to the floor under the unexpected gravity, just as Daeman had done.
Something martian was still seeping through the semipermeable membrane.
The semipermeable membrane of the dome would permit fresh air to enter and allow waste gases to pass out, but would shunt aside anything as thick as a raindrop.
It signaled that the semipermeable force field between the bay and the tinted sea of gases outside was about to fizzle out.