Not sure probably just a good guess
I was a Home Ec major in college many moons ago. During that time I took a number of textiles classes and we had to complete microscopic and other tests to determine the affect of fabric softeners and dryer sheets. Based on my testing I found that fabric softener not only left the item softer but also did not have a "smell" that was still quite strong when it was being placed back in the laundry! We also had the opportunity to document the harmful affect of using fabric softener even once on towels. A real eye opener.
Fabric softener is a liquid added to rise and will penetrate fabrics easier than drier sheets.
