Why Does a Shower Pan Flex or Feel Hollow Underfoot?
A shower pan flexes because the space underneath it is not fully supported. Acrylic pans are moulded shells; if they sit on ribs or a few support pads, the unsupported spans deflect when you step, which is what produces the give, the creak and the drumming sound. Filling that cavity removes the movement.
Step into a cheap shower and you can feel it. The floor moves slightly, and there is a hollow note under your feet. Neither is mysterious — both come from the same cause.
What is a shower pan actually made of?
Not one piece of plastic. The published specification for this class of pan is a co-extruded sheet: the acrylic surface is .185 inches thick, with the top 15% a durable rubber acrylic — pigmented and modified for a high-impact surface, which is the part you touch — and the bottom 85% ABS. The manufacturer’s own spec sheet says the ABS is used because it is “rigid, yet capable of flexibility.”
That sheet is then reinforced with .375 inches of high-density foam, carries an integrated slip-resistant bottom, and is approved to ANSI Z124.1.2.
Why does the support underneath matter so much?
Because a moulded shell is only as stiff as what is behind it. A pan with voids under it deflects when you step; a pan with those voids filled cannot, because there is nowhere for the material to go.
A shower base manufacturer’s own installation guidance puts it plainly: if the mortar base or foam bed under the pan “is weak or missing, you can get flex, squeaks, or even cracks.” Full support means the opposite — less flex, less noise.
Where does the hollow sound come from?
A hollow space under a thin sheet is a drum. Fill it and there is no air left to resonate. Side-by-side comparisons of base materials consistently put composite and acrylic pans at the noisy end and solid-surface and stone at the quiet end — the thinner the shell and the emptier the space beneath it, the more you hear the water.
Does the fill change how the floor feels?
Yes, in a way people notice more in January than in July. Foam is insulation; that is its day job. wedi, who make a foam shower base you tile over, describe theirs as “insulating, creating a thermal barrier that can prevent cold from transferring through the tiled surface.”
Acrylic already holds heat better than tile, and tile is the coldest thing you can stand on. A supported acrylic pan is why the floor is not a shock first thing in the morning.
How is ours filled?
With a dual-compound expanding foam, so the cavities under the pan are filled rather than bridged. Three eighths of an inch of dense foam laminated across the underside, plus the fill, is a different structure from a shell resting on a couple of pads.
Our Warranty
Lifetime warranty covering plumbing, wall systems, fixtures, shower pan, doors and installation. Transferable to a new owner, backed by RenewItHQ, documented in writing. Only exclusion is customer damage.
How to check a pan yourself
In a showroom, step into the pan and shift your weight, then listen. Movement and a drumming note tell you about the space underneath, not about the surface you are looking at. It is the cheapest test available to you and it takes about five seconds.
Talk It Through in Your Own Bathroom
We look at the space, answer the questions this guide raised, and explain the options that fit your home.
Ready When You Are