PVC pipe and elbow fittings make nice square or rectangular panels.
How do you get those contraptions to stand on their own? Just curious. Do you use a 3-way pipe at the bottom corners and construct a kind-of base thingamajig? (I'm always looking for some way to carry a large reflector without a vehicle. Round reflectors, sadly, are the one thing that I've found to be easily collapsible and portable.)
Well, the original LightForm panels, which I have, have internal bungee cords,and break down completely into six separate lengths which you sort of "fold up". The fabric can then be wrapped around the legs, and a velco tie or two lashes the whole thing together. The fabrics have elastics at each corner, and are two-sided. I carry them in some REI (sporting goods store) travel duffle bags, which are like lightstand bags. Those have shoulder straps for slinging over your shoulder. A 42 x 78 inch reflector has MUCH more reflective surface than a round reflector,even a big round reflector.
I'm from the era of before round, collapsible reflectors were invented,and I see the great lengths needed to stabilize them. With PVC panels, outdoors you use turf spikes to anchor them in the wind, and you can make "easel-type" legs to prop them up, or you can use a single, center-mounted, hinged leg with its own turf spike for outdoor use. Since the panels and accessories are joined together with PVC "joining clips", you can put on one, or two, or three "legs" or two or even three "feet" by clipping on what's needed.
There are also factory-made solutions like EC-1 clamps that allow you to clamp onto the PVC panel, then clamp the EC-1 clips to light stands, and then to angle the panel precisely, and then cinch the clamps down to hold the exact angle of the reflector. I have watched a zillion YouTube videos of people using round reflectors,and honestly, they are popular because they are cheap, light, and portable, but they really have serious limitations in how much light they reflect, compared with panels. ROund reflectors present a bit of a physical challenge to hold in position or to affix to light stands at more than one location--simply because the sides of a round reflector that is say 48 inches around are 48 inches apart at ONE, one inch high spot,so you cannot use cheap hardware-store A-clamps ($2.99 each) to clamp a round panel to a lightstand at say 1 foot up from the round, 3.5 feet up, and then six feet up from the ground; since light stands go straight up--if you have straight-sided reflectors, low-tech solutions will work to position a reflector. With a round reflector, you need "grip" equipment, and sometimes, lots of it. Which costs money and is pretty heavy too.
Here's a page that shows just a few panel accessories--not nearly the entire range by any means
Westcott Lighting, Westcott Lighting Accessories Westcott
Here's a company that makes some really nice panels--and note, they do not make any round reflectors--there's a reason you want a flat,straight edge...
Scrim Jim | Westcott Pro Photography and Video Lighting