The function of the bond in moulding sand is that it should make the sand sufficiently plastic for moulding and give it sufficient strength in the green (moist) and dry states after compaction to retain its shape and later to support the weight of the metal. It must do this while still leaving the sand permeable to gases, and it must further retain its strength in contact with the hot metal for a sufficient time for it to solidify, after which it should be sufficiently weak to be readily removable from the finished casting.