The vinyl we use to strap our outdoor aluminum patio furniture has a 90 durometer (measures hardness) and is used almost exclusively in the manufacture of outdoor furniture.
Some differences between old and new vinyl are listed below:
-Older vinyl will become stiff, particularly if it is continuously exposed to the elements
-Has less memory
-Loses softness as plasticizer evaporates from the straps
-Straps are harder in colder weather
-Light colored straps are harder
-Newly extruded vinyl is soft supple
-Possesses considerable memory or resiliency
-Gives with weight placed on it and conform to shape of the weight and returns to straight position once weight is removed
-Straps are softer in warmer weather
-Dark colored straps are softer
It is not possible to predict how long it will take vinyl strap to become harder. So much depends upon the care and conditions under which strap exists. Daily exposure to the sun accelerates the process. There is no way to compare newly strapped furniture to furniture that has been outside for several years.