Balsa wood, which is native to Central and South America, is strong, lightweight, soft wood sheeting. It's scientifically known as Ochroma lagopus, and its name balsa translates to "raft" in Spanish, referencing the wood's fantastic flotation qualities. It's easy to cut and sand, so it is good for wood projects such as model airplanes. Cutting balsa wood accurately is very important so you have clean cuts, regardless of the thickness you choose.
Lay out your balsa wood on a cutting board on an even, sturdy work surface. Measure out the lines where you need to cut, or trace out the shapes you are going to cut.
Secure the balsa sheet to each end to the table to make sure you cut evenly and accurately.
Cut along the edge of your straightedge with the hobby knife slowly and carefully, applying light but firm pressure.
Continue to cut until you have gone all the way through the balsa wood, applying a little more pressure if necessary, but not too much. If you aren't cutting through, repeat the cutting process along the straightedge.
Sand the edges of each piece you cut in order to keep it smooth and unfrayed. You can use a range of sandpapers, from 220-grit to 600-grit, depending on the thickness of your wood.