The length is not the critical specification. The diameter and wall thickness are critical. The diameter specified below produces an optimal sealing surface (between the straw and coupling), while the thickness provides structural integrity to prevent crimping. The diameter and wall thickness work in conjunction to achieve an optimum seal, thus preventing dilution due to air leaks.
Testing in our lab recommends the use of the Dixie JW7. This is a 7.75 inch (196.85 mm) translucent polypropylene straw. Outside diameter is 0.217 in. (5.512 mm), with a wall thickness of 0.007 in. (0.1778 mm). No active chloride is present. There is no absorption of sulfur containing gases, such as would be expected in breath samples.
Packs of 1000 of these straws are available from us, if desired.
It should be noted that bending the straw sideways by more than 15 degrees could cause a break in the seal, thus diluting the sample.