There are many types of insulation out there and each of them comes with various specifications. As you might have noticed already, some insulation knives come with serrations, while others come with smooth blades.
Serrations are ideal for mineral wool insulation and other similar types of wool insulation. On the other hand, a straight and smooth blade is more appropriate for HVAC and mechanical insulation. Since insulation is not necessarily made of hard materials, most knives will manage to get the job done. But if you work in this industry, a specialized blade will save your time and money.