Theoretically, stainless steel is best because it has the lowest reactivity (e.g., it’s less likely to absorb or give off vapors), but flexible plastic tubing is the norm because it’s easier to handle, more affordable, and entirely satisfactory if proper precautions are followed. In general, softer tubing is the more reactive than harder tubing. Semi-rigid Nylon and Teflon tubing are most widely recommended for soil-gas sampling, but others might be acceptable, depending on the applicable guidance.
Most or all Summa-type canisters, and many other sample containers and fittings, are designed to accept 1/4-inch outer diameter (OD) tubing. Cox-Colvin offers 1/4-inch OD, Nylaflow LM, which has superior chemical resistance to generic nylon tubing and is less costly than Teflon. Poly tubing’s chemical reactivity makes it inappropriate for vapor-intrusion sampling, but it might be suitable for high-concentration vapors near source areas. All plastic tubing should be replaced between samples, and stored and handled away from vapor sources. Soft tubing, such as Tygon™, is recommended only for making connections between semi-rigid tubing and other devices, as discussed below.