More material means more weight, but this is usually also synonymous with more power transmission (important when descending!), corresponding flex and sometimes more comfort. How heavy a ski touring boot can be depends strongly on the range of use, your own preferences, the boot construction and the materials used. Under “Which touring shoe do I need?” you will find information about the different areas of use and product categories.
The weight of alpine touring boots plays a significant role, as every gram more makes the ascent more strenuous. Touring ski boots are therefore almost always lighter than conventional boots.