Why does it repeat that she hid them? And here, it says "va'Titmenem" (plural)? In verse 4, it says "va'Titzpeno" (singular)!
Radak: Now it explains how she hid them. 1
Malbim (4,6): Tzafun is in a place that the eye does not see (the opposite of the root Tzafah, to see), even if it is not covered. Tamun is covered with a covering or earth above. When the kings' messengers first came, she did not have time to cover them with flax, only to hide them in a corner where they will not be seen immediately. Also, she could not hide both in the same place, lest the messengers notice them and know that they are the two spies. If they see one in a corner, they would not be concerned, for they know that there were two. 2 In any case, the other would be able to flee. She realized that if they search, they will find them; therefore, she said that spies were here, and just now they fled, so they would rush out of her house to chase them. After the messengers left, she covered them to hide them better, lest they return [to her house] to seek them again.
What are "Pishtei ha'Etz"?
Rashi: It is flax in its stalks. 1
Malbim #1: The stalks were already banged, just they were not beaten, so they were mixed with the wood.
Malbim #2: It is a kind of flax that grows on Etzim (hard stalks) called cotton. Stam flax to which the Isur of Sha'atnez applies, it grows from the ground; cotton is called Pishtei ha'Etz.
What are "ha'Aruchos"?
Radak: The flax was arranged on the roof to dry (Malbim - even before the messengers came. Therefore, one would not suspect that a person is under them). Pishtah is feminine, just like Chitah (wheat); the plurals are Pishtim and Chitim.