Deciding on what kind of wood to burn is a matter of preference, cost, and what you want out of the wood. Below I’ll explain some types that I’ve personally worked with and some that are also options.
Very easy to work with, and practically no grains because the surface is so smooth. No need for sanding and comes in smaller sizes. This can also come with some bark on the sides to give it character, and fine details work great with this type of wood. I use this type the most because I love fine details in my work. This can be found at hobby shops or online although going online can be expensive vs the store.
It is much like basswood in softness, but this has a more plywood look and texture to it. Sometimes theses have sap still trapped inside the wood. The sap can be a challenge because it’s almost like water and doesn’t’ like to burn the surface of the wood. This material is common in hobby/craft stores and comes in sizes big and small. Mostly the small ones look like plaques and are cut into specific shapes.
Yellow pine is a little harder to work with because the grains are vastly different per piece and may need more time to burn. It’s about a half soft half hard wood. It can give cool patterns from the grain but it can also leave inconsistencies while burning. It comes in all shapes and sizes and are sometimes less expensive. This is my personal least favorite wood to burn because of the possible inconsistencies.
I haven’t used poplar personally, but I’ve heard great things about it. It’s such a soft smooth surface and is a higher quality of wood. A lot of people highly recommend it but there is a catch to it, it’s expensive even for little pieces.
When searching for your wood keep an eye out for knots and cracks in the wood. Knots are a pain to hide and burn, and cracks can threaten the stability of the wood. Yes, you may fill in the cracks with stainable wood filler but I do not recommend burning the filler with your tools because it can produce strong fumes. Sometimes you might have to dig to find one that decent, hobby/crafts shops don’t care if there’re knots or cracks on them.