Hardside Sterling 300 Waterbed Mattress

From the manufacturer:

The 300 Semi-Waveless Hardside Waterbed Mattress features 2 layers of back support,
and 3 layers of wave reducing fiber. This is the perfect mattress
for those that like a bit more motion, but still want back support.

With the addition of the 24 mil vinyl, and the re-enforced corners,
this mattress has all of the same features you have come to expect
from a Sterling S-Class Mattress.