Analysis of elements in liquid samples via X-ray fluorescence (XRF) faces challenges due to diverse matrix effects. To address this, the use of glass fiber filters (GFFs) as effective substrates for XRF analysis was explored. The matrix compositions of various commercial GFFs were comprehensively analyzed and compared to assess their applicability in liquid analysis. Most GFFs do not contain heavy elements, exhibit highly consistent filter weights, and have matrix element contents with relative standard deviations (RSDs) below 3%, which are ideal for detecting heavy elements. GFFs were also demonstrated to have superior analytical sensitivity compared to alternative filters. Optimal analytical performance can be achieved by utilizing a 30 mm sample holder, dripping 50 μL of the sample on the uniformly pressed GFFs, and drying it via infrared heating. Most heavy elements showed wide linear concentration ranges spanning over three orders of magnitudes and limits of detection (LOD) lower than mg/L. The results of standard addition and recoveries in natural lake water were promising. Furthermore, GFFs proved capable of verifying the composition and quality of particulate materials. The used GFFs can also be easily regenerated through acid washing for reuse. Therefore, GFFs are optimal XRF substrates for analyzing liquid samples containing heavy metal ions and materials.