I use light wood, as light as I can find. But how light is light? Light wood in the Contest Class is 4.5 lbs per foot cubed, and that is really light. For a 1/16th” x 3″ x 36″ that is around 8 grams a sheet. I have found that the wood from Midwest is common and readily available.
I get wood in batches and 1/16th is my most common size so I get it in batches of 10 per pack. I then weight each sheet on my kitchen scale to find the lightest in the batch.
1/16th x 3 x 36 10 Pack
1/16th x 4 x 36 20 Pack
I try to buy wide sheets an cut them to size later, I even strip my own wood with tools that are suited to the task. Buying bulk makes sense when you build 7 planes a year.
To cut wood in strips you need one of these, they are indispensable. A Balsa Stripper from Master Airscrew. These have been around a long time and as they say, “tools is tools”. They pay for themselves in a short period of time.