Albert Barnes Commentary Exodus 5:7

"Ye shall no more give the people straw to make brick, as heretofore: let them go and gather straw for themselves." — Exodus 5:7 (ASV)

Some of the most ancient buildings in Egypt were constructed of bricks not burned, but dried in the sun; they were made of clay, or more commonly of mud, mixed with straw chopped into small pieces. An immense quantity of straw must have been needed for the works on which the Israelites were engaged, and their labors must have been more than doubled by this requirement.