The best packing material for medium pressures and temperatures is which?

• A. Aluminum
• B. Asbestos
• C. Plant Fiber
• D. Teflon

Answer: (B)

Choosing a packing material depends on its ability to withstand heat and pressure while maintaining a reliable seal. For medium pressures and temperatures, asbestos works well because its mineral fiber structure resists deformation under heat, keeping the packing tight and providing a durable seal in gland or stuffing-box applications. Aluminum isn’t suited for packing since it’s a metal that can’t flex to seal effectively and can corrode; plant fiber breaks down with heat and moisture, losing sealing capability; Teflon offers excellent chemical resistance and can handle high temperatures, but under medium pressures it can creep and may not provide as robust a seal as asbestos in that range. Note that asbestos is hazardous and is largely avoided in modern practice, with safer alternatives used instead.