In the U.S., PEX tubing will bear several of these marks:
Manufacturer's name and product name.
NSF-61. This mark indicates that the pipe meets NSF/ANSI Standard 61 for health requirements.
NSF pw. This mark indicates that the pipe meets both NSF-61 as well as NSF/ANSI Standard 14 for performance, strength and quality control.
NSF rfh. This mark indicates that the pipe only meets standards for radiant floor heating.
ASTM F876 and F877. These marks indicate that the product meets requirements for dimensions and ability to withstand pressure and temperature.
CSA B137-Series 5. This is the Canadian equivalent of the above U.S. standards.
CTS-OD. Copper Tubing Size, Outside Diameter Controlled. This means that the PEX tubing's outside diameter is manufactured to be the same as the outside diameter of the same size copper tube.
SDR 9. Standard Dimension Ratio. Refers to the thickness of the PEX tube wall. This is the standard PEX thickness, where the wall is 1/9th of the outside diameter of the tube.