I have used both.

The regular oil-based poly is what you want. It works well with nylon or polyester fabric.

The fast-drying version is less flexible (probably ok with polyester), easier to scratch/scuff, and in my case, caused "drum tight" polyester fabric to wrinkle up during the coating process.

: I Found Zar Polyurethane about 82 miles from where I live. So I contacted a
: friend who travels through there weekly to bring me some. What he brought
: was 2 different products. Zar Ultra fast drying and the other was Zar
: Polyurethane both are oil based and both are exterior grade. Is there a
: preference? Is one better for nylon skin coating than the other? If
: someone who has used these products I would like to hear your opinion.