Dear Abhinav,

As of my knowledge disposable means one that cant be used for multiple times and reusable means you can use it after cleaning it with proper solvent/reagent.

Would you happen to know what the physical difference in construction is? That is what I really wanted to know. Thanks!

The disposable tubes are often made with from tubing with thinner walls. The reusable test tube is generally made from type 33 expansion borosilicate glass, while the disposable tube is generally made from less expensive flint glass.

You can wash and reuse the disposable tubes, but they are more subject to breakage.