What do you recommend to make an outdoor arch frame and what type of balloons do you recommend? Thanks.
For a walk-through outdoor balloon arch frame it's best to use conduit (at least 1/2 inch diameter) and heavy bases. The bases can be either steel plates or the plastic umbrella stands that you fill with water or sand for stability.
As balloons I would use 11 inch latex balloons inflated to 9 inches. This gives the balloons room to expand without popping (if outdoor temperatures are high).
Don't use pearlized colors; they oxidize faster. Lighter colors are better than dark ones because dark colored balloons heat up more.
The video below explains how to build an outdoor balloon arch frame. The conduit you can buy at stores like Lowe's or HomeDepot. The steel plates and bendable arch cords are harder to find and are typically sold by specialist suppliers like Zephyr.
Zephyr sells their range of products, from bases to extension poles to arch cords at Amazon.