All Webbing is NOT Created Equal
As a former sales manager for a narrow fabrics company, this question really drives me nuts.
Prospects often insisted polypropylene (polypro) webbing was acceptable in cargo safety applications. After drilling down a bit, the root cause for this insistence was always cost. Polypropylene webbing is 
just plain cheap! We always recommended polyester or nylon instead.
A visit to the Web Sling Tie Down Association’s Standard Specification for Synthetic Webbing Used for Tie Downs (WTSDA-T-4) will find no mention of polypropylene webbing. Polyester and nylon are the only two fibers specified.
According to Strapworks.com, “Polypropylene does not have a high abrasion resistance, so it is not recommended for use around rough edges.” However, “Polyester webbing is ideal for heavy loads with high abrasion.”
So what are appropriate uses for polypropylene webbing?
Polypropylene makes great handles for free trade show totes!
But don’t take my word for it.
California Webbing’s website states “Polypropylene webbing is typically used in the medical and fashion industries. Since it has less abrasion resistance in comparison to nylon, it should not be used in weight bearing situations. While nylon and polyester webbing are perfect for holding heavy loads, polypro commercial webbing is more appropriate for belts, bag straps, and life jackets. Polypro is also a less expensive material than nylon or polyester.”
And finally this great chart and statement from shockstrap.com should seal the deal.
The Clear Choice
Polyester webbing is the best material for your tie down straps. Its resistance against abrasion, UV rays, and water make it a better choice for tie-downs than other webbing materials. It is also mildew resistant which makes it an excellent option for snowmobiles and watercraft. The combination of strength and resistance to stretching and abrasion make it ideal for a strong durable tie-down strap.” ~Source: shockstrap.com
I couldn’t have said it better myself!