Packaging such as a blockbase sack (201) suitable for packing of particulate material has an inner bag having two layers of polyethylene, surrounded by an outer bag (201) having three layers of polyethylene. Each bag has a closed bottom and has an open top (208) prior to filling. After filling of the inner bag, the inner bag is closed by a first heat seal along zone (205) in a heat-sealing operation, which can be performed through the outer bag (201) in such a way that the outer bag (201) is not heat sealed to the inner bag at that point. The outer bag (201) is closed by a second seal (207) located between the first seal (205) and the top of the bag (208). A frangible zone (206) is located between the first (205) and second (207) heat seals to enable the outer bag (201) to be removed from the sealed inner bag by cutting or tearing along the frangible zone (206).