Monofilament or fishing line comes in strengths from 2lb up to 80lb. For most designs a weight of 25lb is sufficient. However, for an arch about 50ft long, I would suggest you use monofilament line with 50lb test weight.
Good luck with your arch.
And as always, we would love to see a photo of your balloon decoration (it does not have to be from a wedding, pictures from birthday parties or other events are welcome too).
