Hi Leonard, can you please post a .3dm model file that has your curves and loft result in it? That would help to understand what your hole looks like.

The way the "closed" option works is like the following. Say you have these 4 curves that you are lofting:



When you do a normal loft that is not closed, it will produce this kind of a result, where the surface starts on one profile and ends on the last profile:



Using the closed option will make it pass through all profile in a "loop" type fashion, producing this result:




As far as closing off the holes at the end, that can need different strategies depending on how your shapes are set up. The easiest is if your end is planar, you can cap planar holes by selecting the object and using Construct / Planar .

- Michael