Filtering bacon grease through a paper towel is a common practice used to remove solid particles and impurities from the grease. Most commercial paper towels are made of cellulose fibers and don't contain substances that could leach into the grease at the temperatures involved. However, the quality of the paper towel and any potential additives or processing chemicals could be factors to consider. Some low-quality paper towels might contain residual chemicals from the manufacturing process, such as dioxins or other compounds, which could potentially leach into hot grease. The risk is considered minimal with food-grade paper towels designed for cooking use. The safety of this practice largely depends on the quality of the paper towel, so it might be advisable to use products specifically labeled as food-safe or those made without chlorine bleaching. In a commercial kitchen or for those particularly concerned about potential chemical contamination, using a fine mesh strainer or cheesecloth as an alternative might be preferable.