Quote Originally Posted by gabe View Post
Definition:
ASTM D570-98(2005)
Title: Standard Test Method for Water Absorption of Plastics
This test method covers the determination of the relative rate of absorption of water by plastics when immersed. This test method is intended to apply to the testing of all types of plastics, including cast, hot-molded, and cold-molded resinous products, and both homogeneous and laminated plastics in rod and tube form and in sheets 0.13 mm [0.005 in.] or greater in thickness

Water Absorbtion rate is NOT the information you are seeking.

Permeation rate is the relevant info, also called the WVTR or Water Vapor Transmission rate, and it is usually measured in Grams per mil thickness per 100 sq inches per 24 hours at 73F, 50% relative humidity.

Definition:
WVTR (water vapor transmission rate) is the steady state rate at which water vapor permeates through a film at specified conditions of temperature and relative humidity. Values are expressed in g/100 in2/24 hr in US standard units and g/m2/24 hr in metric (or SI) units.

This info is not usually published by tubing manufacturers, and only available upon request. We spent close to year gathering the data, to come up with the tubing that had the lowest permeation rate for low maintenance (no refills) applications, and came up with another StGobain product called Norprene, which is used in our Quiet Power P180 chassis.

I am the one who mentionned permeation issues to Stew (Cathar) because this type of tubing doesn't work properly with push-in fittings. Given that we are actively working on reducing maintenance (among other things), use of low permeation tubing is therefore critical to us.
Hey Gabe,

Would you happen to know the permeation rate of the more popular brands of Tygon or have a link handy?