"John" wrote

My daughter's partner is getting a new bath fitted soon - what is the
recommendation on the thickness of an acrylic bath that is going to be
used for showering in? I realise that too much flexing will lead to
problems sealing the edges.

When I was re-furbing my main bathroom, the advice received was that the
best strength was in a coated bath.
The argument is that the thicker acrylic baths (say 8mm) actually tend to
get "over-thinned" at tight radius points.
The coated baths start at (from memory) 5mm and have a further coat of
3-4mm.
The one I got was from Aqua Beau with a 25 year guarantee, but I believe
other manufacturers have similar offerings.

Phil