Sounds like a pretty dry topic, but stick around as we sink into the key points about hot tub shell material options—it’s more interesting than you may think.
A little backstory: When we started looking for a hot tub for our home, we were leaning towards a traditional circular wood tub. Not only because wood furniture design and construction is our world (saying we love wood as a material is an understatement) but also we’d seen enough alluring images on social feeds - like below - that the wood hot tub concept was cemented in our heads.
Yet being incredibly familiar with wood we knew there are limits in its friendship with water. Wood expands and contracts when spending time with water, and overall requires more upkeep than we want.
As hot tub buyers, we were seeking easy maintenance, cleanliness, sustainability, energy efficiency, and good looks. Also, we were after a soothing sensory experience. No disco lights, noisy jets, or smelly chemicals.
We were passionate about the idea of quietly* soaking in a tub, listening to the wind or a fire crackling, smelling the fresh air, and our skin resting against a silky material.
By this point we had ruled out plastic. But with so many fibreglass hot tub shells on the market, we’ve included it below so that you, too, can see why we chose to go with a better hot tub shell material.
Here’s what we learned about hot tub shell materials—the good, the bad, and the ugly:
Plastic Rotomold
- Plastic powder is melted and constructed into shapes through rotational molding
- Pros: Matte surface, portable, “plug and play”, cheap
- Cons: Not environmental nor as durable as other options, not energy/heat-efficient, discolours, requires electrical outlet (110v), surface requires cleaning spray, can’t withstand cold temperatures
A perfect example of ‘you get what you pay for’, this tub is cheap for the above reasons. When it stops working or cracks, it retires as a big hunk of plastic at the landfill.
Fibreglass
- Layers of fiberglass-reinforced plastic are formed into a shell shape, then coated with resin for a shiny surface
- Pros: Cheap, lightweight, colour options, finish can be repaired
- Cons: Thin, not durable, prone to fading, scratching and cracking; if not maintained properly it stains or creates mold/mildew
Acrylic
- A petroleum-based thermoplastic created from the derivation of natural glass; melted sheets are molded into shape and have a plastic-feeling shiny surface
- Pros: More durable than fibreglass, colour choices, non-porous, decent insulation if backed
- Cons: Heavier, clunky, not recyclable, not environmentally friendly to manufacture, more expensive
Acrylic shells may include fibreglass, wood, and/or other fillers, adding weight and cost to the hot tub.
In general, plastic shells like fibreglass and acrylic have a more limited lifespan than natural materials: over time they’ll crack or blister and discolour. They’ll need to be replaced, and sent to the landfill.
Wood
- Western red cedar or redwood ‘staves’ (pieces of wood) vertically fit together in a traditional cooperage barrel design with stainless steel tension hoops outside
- Pros: Beautiful-looking natural material, silky feel, can be made deeper than plastic tubs, scented, recyclable
- Cons: Doesn’t hold heat well, higher maintenance, requires cleaning due to bacteria and algae build-up, not leak-proof, swells/contracts (must check & adjust tension hoops regularly), prone to rot and/or weathering, more extensive installation
All-wood hot tubs need to be made from a high-quality lumber - just like barrels - to ensure longevity. However, they require the most upkeep: with water in it, the wood is subject to rapid decay and fungus growth if not cared for properly. Without water in it and left exposed to the elements, the wood can crack and leak.
Over to metals. These are great hot tub material options because they’re welded and are guaranteed to be leakproof. They’re also better conductors of heat.
As natural “green” materials they’re fully recyclable, and their recovery rates are at (or very close to) 100%. But what are the differences between the three metals being used as hot tub shells?
Marine-Grade Aluminum
- Aluminum is a ‘soft’ lightweight metal with favourable properties like strength and high corrosion resistance; when special alloys are added to enhance its properties, it’s known as “marine-grade aluminum” and can withstand constant contact with water and saltwater
- Pros: Low maintenance, durable, easy to clean, hygienic, lightweight (1/3rd of steel’s weight), leak-proof, won’t rust, insulates & maintains heat extremely well, soft against skin
- Cons: Welding quality - if poorly done, tub is weaker
Aluminum is infinitely recyclable and uses little energy to renew the material. (Fun fact: Most of the aluminum produced since the late 1880’s is still in use.) Because of its stellar qualities, marine-grade aluminum is used in shipbuilding & automobiles. If being able to move your tub easily is a factor for you, e.g. in or out of the sun, to different viewpoints, etc., aluminum is lighter and more portable than other metals.
Stainless Steel
- A corrosion-resistant alloy of iron and chromium; sometimes other elements/metals are added to enhance its corrosion resistance
- Pros: Hygienic, unmatched durability & strength, low maintenance, watertight, recyclable
- Cons: Very heavy, tends to be more expensive than aluminum
Stainless steel is popular for luxury custom-built in-ground hot tubs and swimming pools. It looks slick and won’t require moving once installed.
Copper
- A reddish metal that’s malleable and an effective conductor of heat and electricity
- Pros: Highly sanitary, beautiful ‘luxury’ look, lower maintenance, retains heat, fairly durable, watertight, recyclable
- Cons: Very expensive, requires occasional waxing, sensitive to abrasives & acids; it’ll react to water with high acidity and to saltwater
Copper has been used in plumbing for thousands of years, but today’s copper tubs are recycled and often contain an alloy.
For a tub shell, you need a high level of copper (around 97%, which is pricey) and no additives like lead or mercury which can leach toxins into the water.Copper develops a patina—if you don’t like the look of it, you’ll need to strip and polish the copper.
The Best Hot Tub Shell Material
With easy maintenance, cleanliness, sustainability, energy efficiency, aesthetics, and a soothing sensory experience as the requirements, marine grade aluminum is the crystal-clear winner for the best hot tub shell material.
This aluminum alloy comes in different grades from 3000 to 6000. The best marine-grade aluminum is either 5000 or 6000 series—both are meant to withstand constant exposure to water and weather. GOODLAND uses 6061 for our hot tub shell since it offers extra strength and excellent corrosion resistance, perfectly weathering the elements across all seasons. It's also easier to weld and finish, leading to a more premium-looking product.
Aluminum as a shell additionally heats up more quickly, won’t get funky and require cleaning or chemicals when in contact with water for some time, and is lightweight for portability.
In our GOODLAND wood fired tub design (shown above), we added Reflectix Insulation around the aluminum tub to stop radiant heat loss and for winter hot tub use. We topped this with beautiful western red cedar planks to further insulate it, and in contrast with the metal, it looks pretty stunning.
We incorporated comfortable red cedar recliners that can be easily removed when you’re not in the tub, preventing slime build-up and keeping the tub in low maintenance.
Learn more about the considered design elements of this wood burning hot tub, or see the Resources section of our Journal for more 'how tos' and 'whys' about our hot tub.
Did we miss answering any of your questions about hot tub shell materials? Shoot us an email, we’d love to hear from you.
*When our kids are sleeping.
