I just have found these interesting notes:
Tub types:
CAST IRON - Best quality.
Pros: Durable, easy to clean, quiet, no flex (mortar-bed not needed).
Cons: Most expensive, Heavy-weight (not an easy install for one person), absorbs heat until warmed, generally shallow depth.
STEEL - 2nd best quality
Pros: Durable, Least expensive, Light-weight, easy to clean, no flex (mortar-bed not needed), generally the deepest, appearance is same as cast-iron.
Cons: A bit tinny-sounding and dosen't hold heat well.....but, here's a tip to fix both issues: Turn the tub upside-down. Cut pieces of 1/2 inch thick foam-board to fit the bottom, sides and ends of the tub. Glue it to the tub with foam board adhesive, fill odd-spots with spray-foam. No, it won't look pretty, but it will be quieter than cast iron and hold heat better than fiberglass. DO NOT try to short-cut by using fiberglass insulation. Any future water leakage will trap moisture and cause mold. Foam board will not. If you do this tip, then there are NO cons to a steel tub.
FIBERGLASS - 3rd best quality
Pros: Durable if installed with mortar bed, moderate cost, light-weight, moderate cleanability. Note: cleanability improves if you spend more to get an acrylic-skinned fiberglass tub. Available as one, two or three-piece tub-shower units that allow you to skip the tile process if it's going to be used as a shower.
Cons: Typically priced between cast iron and steel. Cracking near drain is common if bedding step is skipped, generally shallow depth.
VARIANTS:
Kohler Sterling - made of Vikrell plastic. It's tough, has a nice finish and doesn't require bedding, tub can be purchased with or without walls.
American Standard Americast - a plastic backed steel tub with reduced tinniness and improved heat retention. (The steel tub tip above will yield a final product as good or better at lower cost).
Final notes:
Be careful. I've seen dropped tools damage them all.
When you install the new one, you're going to be standing on that new surface to work on the walls. Keep it vacuumed free of debris and lay a piece of clean carpet upside down in the tub to stand on. Don't use the stupid piece of cardboard that comes with the tub.
Install the tub drain (regardless of tub type) with a high quality silicone caulk containing mildew inhibitors and NO acrylic or latex. Apply a bead heavy enough to see it squeeze out between drain ring and tub surface. Allow to cure before exposure to standing water. Do not use "plumber's putty." It makes a poor drain seal as it will dry out and shrink, fracture and start leaking.
If you choose cast iron or steel and decide to tile, be sure to use backerboard behind the tile. Do not use drywall or greenboard. Seal the grout to prevent future mildew problems.
No tub will look good after 5 years if it's abused, so don't use abrasive cleaners on any of them.
Only question I have, if I purchase this product
Ok I might go with CAST IRON, but how can I find out if my floor upstairs is able to support it? Filled weight lb 870.0 vs 650 lb for Acrilic...