Como Pureferret observa em sua resposta a esta questão ,
Os parafusos Blaster são feitos de plasma, não de luz. Veja aqui .
Blasters are a considerable improvement over the archaic laser design. Instead of a coherent beam of light, the blaster fired a compressed, focused, high-energy particle-beam that is very destructive, commonly referred to as a "bolt". (Star Wars: The Complete Visual Dictionary)
Então, como as respostas a esta pergunta apontam,
The 'blade' is a magnetic 'bottle' containing the plasma generated by the lightsaber. It generates a strong electromagnetic field. This means that the blade will have a little resistance to motion when in the presence of ferrous metals (most of the time, in SW). The blade will, therefore, 'bounce' off some metallic substances, even as it melts them. (The duel in ESB has some good examples.) The dense magnetic bottles are certainly the reason the blades 'bind' on each other rather than passing through each other.
Por fim, conforme observado aqui ,
When cutting through dense material, the immense electromagnetic field generated by the arc caused resistance rather than letting solid matter enter and interrupt the arc. This gave the blade a feeling of being solid when immersed in dense material. Rarely, some solid materials could actually pass through the electromagnetic field and short out the arc. Other electromagnetic energy fields and coherent energy were also repelled by lightsabers' arcs. These include most force fields, blaster bolts, and other lightsaber blades. (Wookiepedia: lightsaber)