Use a physical barrier for small openings. Packing and retention matter as much as the material.
Check around cool pipes, including the underside. Repair leaks and damaged surrounding material first.
Cut and shape purpose-made exclusion mesh carefully. Loose metal strands can scratch skin.
Fill the small gap completely. A loose surface tuft can be moved aside.
Follow the sealant instructions. Keep conductive mesh away from wiring and never block vents or hot flues.
Choose securely fixed metal plates or suitable hardware cloth. Mesh stuffing needs support.
Learn where copper mesh fits and how to inspect the finished repair.