You are correct that the Large Folding at the OUSA conventions have used Photo Backdrop Paper which is heavy. Large folding is physically demanding on the folder. Some large models need extra internal support to stay upright - as the paper will not hold up its own weight.
Origami USA the Source has two types of Large Paper which will need cutting to get the squares; One is on Clearance Sale. Origami USA - The Source https://origamiusa.org/catalog/paper ELEPHANT HIDE SINGLE COLOR LARGE SHEETS - 10 sheet pack SKU: P10-EHLG Tough, tear-resistant, parchment-look paper with a smooth finish. This is the same paper as "Elefantenhaut" and "Wyndstone Marble." This heavy paper is ideal for wet-folding and tessellations. Single color packages include 10 sheets. Specify color: light brown, chamois, light grey, or light blue. Same color both sides, 110 gsm weight. See review at http://origamiusa.org/thefold001_paper. 19.5” x 27.5” 10 sheets TANT LARGE SHEETS ON CLEARANCE SKU: P31-TLS 70gsm sheets 31 inches by 43 inches (788mm by 1091mm). Same color on both sides. Creases accurately and reverses well. Great for dry sculpting and good for wet-folding. Surface has enough texture to provide friction for holding together modulars. Price is per sheet. Specify color: Yellow, Grey, Black, Purple 31”x43” 1 sheet Another source that I have used in the past, was Bemis-Jason Fadeless Bulletin Board Paper. The name has now changed to Pacon. It comes in rolls of 24 inch and 48 inch. It is colored on one side and white on the other. It folds like origami paper but relatively thicker given the sizes. I have gotten it at Dick Blicks or Teacher Supply Stores. Fadeless Art Paper Rolls — Available in 24" (61 cm) and 48" (122 cm) widths, each roll is packed in a dispenser box. This fade-resistant, acid-free, 50 lb (74 gsm) art paper has a smooth matte finish color on one side, white on the other side. Fadeless Art Paper is excellent for paper sculpture, bulletin board work, signs, posters, and backgrounds. ® Pacon is a registered trademark.® Fadeless is a registered trademark. Good luck with your search! See you at the OUSA convention. Mark Kennedy
