The ‘Web Sling and Tie-Down Association’ conducted two long time exposure test study on the degradation effects of polyester- and nylon web sling when exposed to sunlight. The first test was done in 1981, and the second test series was done between 1997 to 2004. The full test report is published by WSTDA, a copy of which can be obtained by Unirope.

One of the main conclusions reached by WSTDA:

"The polyester samples tended to undergo most of their strength loss during the first twelve months of exposure and then leveled off approximately a 30% loss in strength. The nylon 6 and nylon 6.6 sample showed a general trend of consistent strength loss over the entire 36 months exposure period, with strength loss levels approaching fifty to sixty percent after 36 months for some sample tests."

Based on the test results and conclusions reached, Unirope has decided to discontinue the use of NYLON webbing material for Boat Lifting Slings.

However, it must be noted that, although Polyester webbing seems less affected, even polyester slings will undergo a significant strength loss leading to a DECREASE in strength. Consequently, the DESIGN FACTOR for such slings will DROP from a 5:1 value to at least a value of 4:1!
Web Sling & Tie Down Association:

The following is a WARNING as published by the ‘Web Sling and Tie Down Association’ in their ‘Recommended Standard Specification for Synthetic Web Slings, WSTDA-WS-1, version 2004’:

5.3.5 Environments in which synthetic web slings are continuously exposed to ultraviolet light can affect the strength of synthetic web slings in varying degrees ranging from slight to total degradation.

CAUTION: Degradation can take place without visible indications!
  1. Factors, which affect the degree of strength loss are:
    1. Length of time of continuous exposure
    2. Web sling construction and design
    3. Other environmental factors such as weather conditions and geographic location.
  2. Suggested procedures to minimize the affects of sunlight or ultra-violet light.
    1. Store web slings in a cool, dry and dark place when not being used for prolonged periods of time.
  3. Some visual indications of sunlight or ultra-violet degradation are:
    1. Bleaching out of web sling colour
    2. Increased stiffness of web sling material
    3. Surface abrasion in areas not normally in contact with the load.
  4. PROOF TESTING WARNING
    1. Slings used in environments where they are subject to continuous exposure to sunlight or ultra violet light shall be proof tested to twice the rated capacity semi- annually, or more frequently depending on severity of exposure.