The PTFE is “cast” for the AQR™ septa in the screw caps which includes our catalog number 9509S-10C-B as well as many other AQR brand screw and snap caps.
It is much easier to control the quality of “cast” PTFE over the “skived” PTFE which results in much better reliability and performance from batch to batch.
The most important advantage of cast PTFE over skived is that this type of PTFE is less likely to have small, unseen pin holes from microscopic bubbles in it that results when skiving. This can be important when leaking of volatiles is important as the cast PTFE is a better barrier or when leaching from the silicone rubber into your sample is important to avoid.
Also, it is important to note that the silicone rubber used in this line of autosampler caps is that the silicone rubber is “platinum cured” as opposed to most commercially available caps which are “peroxide cured”. The platinum cured rubber is the purest available and extremely low in contaminants.