The C2 elevates the tub interior to 316-L marine-grade stainless steel at 14-gauge thickness — a meaningful and deliberate material upgrade from the 304 steel used in the C1. The grade difference is significant in a cold plunge context. Standard 316 stainless adds molybdenum to the chromium-nickel alloy of 304, which dramatically increases resistance to pitting corrosion, crevice corrosion, and chloride attack — the specific types of corrosion that are accelerated by cold water, ozone chemistry, and the mineral content of tap water over years of continuous use.

The "L" designation in 316-L means low-carbon, which further improves the steel's resistance to sensitization — a form of corrosion that occurs at weld seams when carbon precipitates out of the alloy during high-temperature fabrication. In a welded stainless steel tub, 316-L ensures that every seam, corner, and weld point has the same corrosion resistance as the flat plate material, eliminating weak points. 316-L is the recognized standard for marine hardware, medical implant manufacturing, pharmaceutical processing, and any application that requires sustained corrosion resistance in chemically active environments.

The C2 tub walls are described as extra-thick, providing structural strength and thermal mass beyond what the 14-gauge specification alone delivers. The interior is contoured at a 20-degree ergonomic slope, bringing bathtub-style ergonomic geometry into the cold plunge form — so the client settles into a naturally supported, reclined position rather than sitting rigidly upright, which reduces muscle tension during sessions, allows for longer and more consistent immersion, and contributes to a more comfortable and repeatable daily protocol. Interior dimensions for the Standard 60" configuration measure 60.0" L × 24.0" W × 21.25" H, and the XL 66" configuration measures 66.0" L × 24.0" W × 21.25" H. The C2 is suitable for users up to approximately 6'4".

The C2 frame shares the same marine-grade plywood core and Line-X® 16-mil polyurea exterior as the C1, with the same structural philosophy and weatherproofing standards. What differentiates the C2 frame architecturally is two things: its wider footprint and its end deck configuration. The C2 frame measures 92.5" L × 43.5" W × 28.5" H for the Standard 60" tub, and 98.5" L × 43.5" W × 28.5" H for the XL 66" tub — the additional width (43.5" versus the C1's 37.5") is a function of the end deck, which is a built-in platform positioned at the end of the tub that provides a comfortable and natural stepping surface for entry and exit, a surface for accessories or equipment, and an architectural element that gives the C2 a more complete, finished presence than a tub-only unit.

Where the C2 frame program significantly expands beyond the C1 is in its wooden deck options. BlueCube hand-selects and finishes premium hardwood decks at their Oregon facility, available in walnut, mahogany, white oak, white maple, and cherry. These are solid hardwood decks crafted and finished to a furniture-grade standard — not veneer overlays or composite wood products.

The wood top fundamentally transforms the visual character of the unit, shifting it from a wellness appliance into an architectural object that belongs in a designed space. Custom frame finish options include any Sherwin-Williams color in Line-X®, the ability to order the frame prepped for on-site cladding (sanded and moisture-sealed to accept tile, travertine, marble, cedar, or any architectural finish applied by the client's contractor), custom CNC-cut logos in wood, laser-engraved stainless steel panels, powder-coated screens, foot pegs, and reverse plumbing/vent configurations for non-standard installation orientations.

The C2 insulation system parallels the C1 — marine-grade plywood frame as a natural thermal buffer, Line-X® 16-mil polyurea coating as a continuous weatherproof and thermally resistive shell, and an insulated spa cover with child locks included standard.

The extra-thick tub walls of the 316-L stainless interior also contribute a greater thermal mass than the C1's standard walls, meaning the water temperature is more stable and recovers more quickly after a session adds heat load. The end deck configuration of the C2 also means the cover sits over a more completely enclosed tub opening, which improves the seal between the cover and the tub rim for better heat retention when not in use.

The C2 uses pool and spa-grade Schedule 40 PVC in 1"–1.5" diameters, hand-insulated throughout, and pressure-rated for high-flow, high-pressure operation. The larger 1.5" primary plumbing diameter in the C2 is specifically sized to support the higher volumetric flow rates demanded by the dual-pump RiverMode™ Plus system — two pumps each moving 25.6 gallons per minute require plumbing that can handle that combined flow without restriction or pressure loss.

The same accessible mechanical layout as the C1 makes all components serviceable by any licensed plumber or pool and spa technician without specialized training or proprietary tools.

The C2 meets and exceeds commercial-grade standards across every metric. It is rated for up to 100 plunges per day, sustaining 11–15 plunges per hour while holding water temperature within 4°F of the set point across consecutive sessions. The 1.5 HP commercial chiller provides greater thermal recovery capacity than the C1's 1 HP unit, making the C2 more capable of handling sustained heavy use in a commercial context.

The BlueCube commercial flow rate for the C2 is specifically cited at 26.5 gallons per minute for rapid cooling and filtration, meeting DOH-compliant standards for regulated high-traffic environments.

The Commercial Upgrade Package for the C2 includes AOP or automated chlorine drip sanitation, a commercial-grade integrated skimmer for continuous surface debris capture, alternative non-metal tub materials, and complete DOH documentation and build sheets for health department approval across most jurisdictions.