The Firmament is mentioned in the creation account of Genesis and throughout the bible.

It is paramount to God’s creation and word. Without the firmament there would be no air to breathe.

If the sky were a vacuum, the atmosphere would immediately fill the available volume i.e. the ENTIRE volume of space.

The Firmament and our gas pressure (our atmosphere):

The formula for Pressure is P = F / A.

Pressure is a force over an area. The reason we are breathing gas pressure is

because the gas molecules are bouncing of the (area) walls of the container aka the Firmament.

Just a few bible verses:

God called the Firmament heaven. And there was evening and there was morning, a second day. Genesis 1:8

Then God said, “Let there be lights in the expanse of the heavens to separate the day from the night, and let them be for signs and for seasons and for days and years. Genesis 1:14

Covering Yourself with light as with a cloak,
Stretching out heaven like a tent curtain. Psalm 104:2

For the choir director. A Psalm of David.
The heavens are telling of the glory of God;
And the Firmament is declaring the work of His hands. Psalm 19:1

The Firmament

In Hebrew, the word is “Raqiya” or “Rakia”. In the bible, the Firmament is a solid expanse.

Source: Blue Letter Bible (Hebrew and Greek Lexicon