Polyethylene XRF sample cups offer the option to vent cells for pressure equalization purposes through the rotation of a snap-on closure. These are used with X-ray instruments with single or automatic multi-sample changers, and for other equipment requiring a shallow sample cup with a large sample excitation area. These sample cups are designed to eliminate the need for trimming extraneous thin-film sample support material, and offer top sample loading. Snap-on rings in some models firmly secure the thin-film to the cell.