What is the difference between colloidal solutions and true ones?

A colloidal solution is a heterogeneous mixture in which the particle size of a substance is intermediate with respect to the true solution and suspension, i.e. from 1 to 1000 nm. Fire smoke is an example of a colloidal system in which tiny particles of a solid float in the air. Like true solutions, colloidal particles are small enough to be invisible to the naked eye. They pass easily through filter paper. But the colloidal particles are large enough to be blocked by parchment paper or animal membranes.