Wet cardboard is very heavy here. I use packing boxes and they seem to work quite well for me. And it is faster than laying down several layers of newspaper for me. But that's just me though. I have also used newspaper, but it tends to rip really easy which can be a problem. I have a dog that runs around when we are sometimes laying down newspaper. I spray water on the layers of newspaper as I am laying them down, but stepping on it can be a bit of a challenge to try not to rip it by accident, which is why I started using cardboard. Cardboard (and newspaper) also attracts earthworms! (Which I want in my yard!)
What lies behind us and what lies before us are tiny matters, compared to what lies within us. Garden Rooms and Becky's Budget Garden