Many Hot Tubs, particularly the cheap imports form the east, are constructed using the cheapest possible methods reducing the cost as opposed to constructing to a much higher standard of quality. Often made by unskilled workers who are unsupervised working in rather harsh conditions of a slave factory.

Like wise this cost cutting or trying to make a Hot Tub from the cheapest way can also apply to those who are making the largest numbers of spas in the world.

Many Hot Tubs are made using a fully foamed approach some times known as the "fully foamed" or "foam filling" system this is, very much, an out of date production method but is still in use by many makers as it is one of the cheapest forms of construction.

In this cheaper system, the shell or Tub of the unit is made from thinner sheets of acrylic or ABS plastic the Tub is then plumbed and piped with all the required pipes etc.

Then the cabinet that surrounds the Shell is pumped full of expanding foam to give the shell its support.

This is a much cheaper method of construction as it means that the manufacturer is able to use cheap foam, (instead of fibreglass), to support the shell, rather than building a shell with sufficient strength in the first place!

There are various disadvantages of this system of construction:-

1) Sprayed in polyurethane foam degrades over time, such that there is a decrease in the insulating value.

2) The settling and expansion/contraction of the foam can actually cause leaks in the plumbing.

3) Lastly and most importantly you cannot of course access any of the internal parts of the spa in the case service is required. Effectively then the most serious downside to this cheaper method of construction is that there is, more or less, total inability of serviceability during the lifetime of the spa. Not only is the plumbing but also the jet fittings are buried in to the expanded foam. This of course means that, leak detection is more or less impossible with out de-constructing the Hot Tub and removing substantial amounts of foam...

If a fully foamed spa should leak from the rear of a jet fitting then that water seepage may not become apparent until the foam has become extremely wet and soaked through.. The most modern productions methods would be to use some foam to support the pipe work but not to indiscriminately blast, the spa cabinet full of polyurethane as there is no proven benefit to this practice and it actually causes dealers and customers a severe service/access headache.

I have heard it said that some manufacturers fully foam their spas so as to keep the noise of the pipes down - must be a badly designed tub if its that bad.

This is a bit like perhaps building the electrics and heating systems in a car or in a house in to sold foam. Simply because you have been told it will keep the noise down and in any event it will not need servicing . well its not something I would do or believe nut many hot tub manufacturers would have you believe ot to be true.

Is your heating ,plumbing and electrical systems at home, hidden in solid foam because you've been told it would never need servicing? That does not sound like a good idea to me ? Many spa manufacturers would have you believe that it was! Or perhaps have the bonnet of the car stuck down with cement so you couldn't check the oil or water would that be a good idea?