This is actually this procedural polka dot material https://blender.stackexchange.com/questions/50730/procedural-polka-dot-pattern-with-cycles

But I mixed it with a transparent shader in order to achieve a fishnet material.

From the Mapping node you can scale the holes. The X and the Y axis control the amount of the holes. If they have the same value, the holes are circular. But you can use different values on the X and Y to stretch the holes and make them oval. The Z axis controls the diameter of the holes (use values mostly between 0 and 1.5). Or you can use the Color Ramp for that and never touch the Z axis.

And of course you can change the color and how the material looks like from the Principled shader.

If you want to use this material for an already UV unwrapped model, then change the Texture Coordinate that is plugged into the Mapping node from 'Generated' to 'UV' .

P.S. You can play with the Gradient Texture and change it from spherical to diagonal or linear for example to achieve other patterns. And then delete the transparent and mix shader and plug the color ramp to the color input of the Principled shader to color your pattern at will.

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