Re: Advise on buying new tub?
Cast iron is definitely the most durable, but if the porcelain enamel is chipped repair is more difficult than for acrylic fiberglass.
(By the way, "acrylic" and "fiberglass" are generally the same thing; the glass fibers are bonded together with acrylic resin and covered with an acrylic "gel coat". Acrylic by itself probably wouldn't be strong enough.)
If you do go with acrylic fiberglass, consider the thickness of both the fiberglass and the gel coat -- the thicker the better. A high-quality unit will weigh nearly as much as cast iron. Gel coat that is at least 1/8" thick will be less likely to chip and crack. Thicker fiberglass will yield a stiffer unit. The base of the unit must be set in mortar or concrete to prevent flexing from the weight of water and users. Some people use rigid expanding foam (spray foam) instead of concrete with reasonably good results, though not all manufacturers will warranty this method.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.