I've used the acrylic yarns [not nylon] most of my life, and have given many sets of acrylic potholders to my friends. My pattern, original to me, is to use 2 afghan-stitch squares crocheted together - nice and thick.
The only time any of my potholders have melted is when I tried to use my potholders for hot pads so I could take a hot pot and set it on the countertop. Then things melted enough to become unusable.
Otherwise, I've had the same 7 potholders for well over 11 years. And I used a darker yarn so stains won't show so much; and the acrylic yarn can easily be tossed in the washer and dryer - this gets done quite frequently.
Wool and cotton are great choices if you are going to make your potholders double as pads for oven-hot or burner-hot pots and dishes; these don't wash nearly as well as acrylics do.
Hope this helps,