The straw was used either to mingle with the clay, that it might not be too brittle; or to cover the clay when it was formed into bricks, that the heat of the sun might not dry them too much, which might easily be done in that hot country; or for fuel, either wholly or in part, to burn their bricks with, straw being abundant there, and much used for that purpose.
Related Commentaries of Exodus 5:7
Exodus 5:7
7 Ye shall no more give the people straw to make brick, as heretofore: let them go and gather straw for themselves.