No — never pour boiling or very hot water into a Grayl filter. It can damage the purifier cartridge and bottle. Always let water cool to below 120°F (49°C) before filtering. Boiling water can degrade the carbon, plastic, and filter media, making the purifier unsafe or ineffective. If you boil water to sterilize it (e.g., in the backcountry), just let it cool before using your Grayl.