Abstract: A protective liner for removable insertion into a trash bag or other container comprises an essentially rectangular sheet of strong, flexible material The dimensions of the liner are tailored to the dimensions of the bag or container into which it is to be placed. The preferred embodiment is provided with locking means at one corner, a rounded adjacent corner and is made of one millimeter thick polyethylene. The preferred embodiment is particularly adapted to be suitable for use with the broad category of trash bags known as 30-gallon trash bags.In use, the liner is rolled along its longer axis into a cylinder with an effective diameter smaller than that of the associated container, the overlapping material is pinched together, the cylinder is inserted into the container, and compression is released (allowing the liner to expand to fill the container). Optionally, the liner is locked in place. The container may then be filled with little danger of puncturing the sides.