The question of the firmament (Genesis 1:6) has also generated various interpretations, but we need to keep in mind that the Hebrew word (raqia) means simply "expanse," as in "a great expanse of water between California and Hawaii." An essentially synonymous English term would be "space." And just as "space" can be used to refer to space either as an entity or to a particular space, so likewise for the word "firmament."
There are at least two—probably three—special "firmaments" mentioned in Scripture. The most exalted firmament is under God's throne (Ezekiel 1:26). Also, there is an atmospheric firmament, where birds fly, and a stellar firmament, where the stars are (Genesis 1:20,14). There are likewise three "heavens" (note II Corinthians 12:2), and it is significant that God called the firmament "Heaven" (Genesis 1:8), where the Hebrew for "heaven" is actually a plural noun (shamayim), frequently translated "heavens." These distinctions are not often made by creationists when discussing a particular firmament (or space, or heaven), but they are Biblical, and it is important to take careful note of the context in each case.
This brings up another controversial subject, the canopy theory, the essential component of which is "the waters which were above the firmament" (Genesis 1:7). If the particular firmament (or space, or heaven) in mind here is the atmosphere, and if the waters were in the vapor state, then many Biblical facts and scientific relationships are beautifully explained. However, there are certain scientific difficulties that are still unresolved, and there is again a temptation to abandon the theory because of these.
from http://www.icr.org/article/503/
Interesting.
Thanks!