A liquid filter element includes a circumferentially extending array of pleated filtering material. The end sections of each of the pleats are folded over and crushed together, and are embedded in a plastic plug to form a rigid link extending substantially transversely with respect to the array to thereby strengthen the array against inward radial collapse in response to liquid pressure acting on the array. A process for making the element is disclosed which includes the step of forming a circular array of pleats, applying pressure to the end sections of the pleats to crush the pleats and rigidify them, and then bending the rest of the array about the rigidified portion to form the thimble-shaped filter element.