Softbox support rods are commonly made from fiberglass or aluminum. For DIY replacement, fiberglass is a very practical choice because it has some flex, which helps when tensioning a softbox into shape. Tent poles are also a good source of suitable rods, since they’re designed to be lightweight and slightly flexible.

Another DIY-friendly option is fiberglass fish rods sold for electrical wire pulling; they come in long sections and can be repurposed for softbox builds.

Carbon fiber may work, but it’s generally less commonly mentioned for this use and may be less forgiving if you need the rods to bend under tension.

If you’re building a larger modifier, you might also consider an umbrella-style softbox design, which uses the existing umbrella frame structure instead of separate support rods.

In short: for replacing or building softbox rods, start with fiberglass or aluminum, and check tent poles or fiberglass fish rods as easy DIY sources.