Rashi: It is a scroll.

Radak: It is a letter.

Malbim: It is a parchment.

Radak #1: Perhaps there were many words; their essence was "Lemaher Shalal Chash Baz."

Radak #2: The big Gilyon was a metaphor for Eretz Yisrael. Just like the Gilyon was big and only a few words were written in it, so Eretz Yisrael is vast, and its inhabitants are few, for the 10 tribes were exiled and the majority [of Eretz Yisrael] was destroyed.

Malbim: The parchment is thick and hard.

Rashi: With a writing tool, [write in a way] that anyone can read it quickly, even a simple person who is not a Chacham. This is like Targum Yonasan - an explicit writing.

Radak: Do not think that the command to write is only in the prophetic vision. Rather, be should physically write due to the Nevu'ah. What is written b'Cheret Enosh in a Nevu'ah is not truly b'Cheret Enosh, for it is not a true action, just like Yeshayah going naked and barefoot (20:2), and Hoshe'a marring a Zonah (Hoshe'a 1:10) and Yechezkel shaving his hair and beard (Yechezkel 5:1) were only in prophetic visions.

Malbim: He commanded him to draw in the parchment forms of men fighting and plundering.

Rashi: To hasten Sancheriv's coming, and to plunder all the wealth of the 10 tribes, and to hasten Nebuchadnetzar after him, to plunder Tzidkiyah and his generation.

Radak: "Chash Baz" is a repetition of "Lemaher Shalal" in different words, to strengthen the matter and hasten it.

Malbim: Just like Hashem commanded to call the first son Imanu'el for a sign that He will be with us, He made a Siman of the fall of Retzin and Pekach via the scroll and the second name. From 7:17-25 was a Ma'amar Musgar (parenthetical comment) that because [Achaz] did not trust in Hashem, and requested help from Melech Ashur, the sign of Imanu Kel will not totally come in his days. Melech Ashur will approach Achaz. The sign will be fulfilled totally in the days of Chizkiyah, like it says in Perek 9. Soon after this Nevu'ah, Aram and Efrayim will be plundered.