Unfortunately we haven't got round to do a page with step-by-step instructions for spiral arches yet. However, the basics are the same as for the "Spiral Column". To create an air filled spiral arch you need a more flexible rod than we used for the column in order to shape a nice frame. And you need to make two sturdy bases (how to make those bases yourself is also explained on our site).
I've searched the various balloon decorator forums and groups I am part of and I found one resource that you could check out for instructions on how to make a helium filled spiralled arch.
The advantage of a helium filled arch is that you don't need to build a solid frame. The downside are the higher costs and the shorter lifetime of a helium filled design:
