When the plastic belt was introduced it was only natural that it was seen as a replacement for the steel belt. In a way, it was especially in the applications where steel was used simply because none was available. Often, in the first case, the steel exceeded specifications. The existence of plastic tapes expands the range of tapes and offers new possibilities. But to take advantage of these opportunities, you need to know how it differs from steel.
For steel, elongation is not a key property. With a plastic belt, this is a consideration as long as it stays within its working range. A more important consideration with plastic strapping is stretch recovery. How hard will the strap try to regain its original length after the tension is applied and the strap lengthened? Timber loads are a good example of good steel-to-polyester conversion showing how all strapping factors work in a real application.
While polyester often has a lower shear strength than steel, its ability to stretch and recover often still makes it more effective than steel for timber loads. Let's get back to our rubber band analogy. Wood is heavy, wobbles in transit shrink as it dries, and cargo often settles in transit. With this in mind, a strong but flexible rubber band (hereafter referred to as #1) works better than a stiff rubber band. Volume (#2) that cannot be extended and restored. On impact, elastic #1 will stretch and spring back, while elastic #2 may break.
If the load shrinks or settles, elastic #1 will spring back while holding the load in place, while stiff elastic #2 may loosen, leaving the load unprotected. too focused on breaking strength. Tensile strength is an important factor, but lower strength polyester can often carry a load better than higher strength steel because it can stretch and recover (like a rubber band).