What is the best molding way to mass produce bar soaps?

Here is the answer to your next soap making question:

It depends on whether you intend to produce 5kg batches, or 50kg.

for a 5kg batch I would suggest plastic pipe, round bars can be made using 2.5 inch to 3 inch rainwater drains cut into 12 inch lengths, I have also discovered some 2 inch by 4 inch rectangular ducting which makes a more normal soap bar shape and can be used in the same way.

For larger batches, I would suggest you check out this website, they are a Hawaiian company who produce handmade soap on a larger scale and this page has a video which illustrates the principles very well - check out the use of an old drawer as a mold: http://hawaiianbathbody.com/story.html

More soon.