The C3 tub interior uses 316-L marine-grade stainless steel at 14-gauge thickness with extra-thick walls — identical in material grade and construction standard to the C2. This is the highest-grade stainless steel specification in the standard C-Series, providing the same superior pitting and crevice corrosion resistance, the same low-carbon weld-seam integrity, and the same refined, non-porous interior surface as the C2. The C3's material specification is not differentiated from the C2 — what differentiates the C3 is its tub size.

The C3 is available in two configurations: a 66-inch tub interior (best suited for users up to 6'9") and a 72-inch tub interior (for users 6'9" and above, or for commercial environments maximizing user comfort and versatility). Interior dimensions are 66" L × 24" W × 22" H and 72" L × 24" W × 22" H respectively. The additional 6–12 inches of length compared to the C2's 60" or 66" interior is not a trivial comfort difference — for taller users, it is the difference between a session where legs are forced into an awkward position and a session where full natural submersion, leg extension, and body repositioning are all possible.

For clients who use cold immersion daily as a performance protocol, that positional comfort directly impacts the ability to maintain the session duration and consistency that the protocol requires. The C3 can support full head submersion in addition to neck-depth immersion, which is relevant for clients whose protocols include head immersion for neurological and scalp-level cold exposure. Weight is approximately 750 lbs empty — slightly heavier than the C2 due to the larger tub volume.

The C3 frame uses the same marine-grade plywood core with Line-X® 16-mil polyurea coating as the C1 and C2, built to the same structural and weatherproofing standard. The architectural differentiation of the C3 frame is its side deck configuration — where the C2 features an end deck at the far end of the tub, the C3's deck runs along the long side of the unit, providing a wider and more naturally accessible entry and exit surface.

For a 66" or 72" tub, a side deck is a meaningfully more practical design choice than an end deck, as it reduces the distance a user must step across when entering and allows for more comfortable positioning during entry and exit — particularly relevant for taller users for whom the longer tub is designed.

The C3 frame exterior dimensions are 72" L × 48" W × 29" H with the 66" tub and 78" L × 48" W × 29" H with the 72" tub. The 48" width is the largest in the C-Series and is driven by the side deck depth added to the tub width. This footprint should be carefully accounted for in space planning, particularly for indoor installations.

The full range of C2 finish, wood deck, and cladding customization options is available on the C3 — walnut, mahogany, white oak, white maple, and cherry wood deck options, any Sherwin-Williams custom Line-X® color, prepped-for-cladding ordering for tile, travertine, marble, cedar, or other architectural finishes, CNC logo in wood, laser-engraved or cut stainless steel panels, powder-coated screens, foot pegs, and reverse plumbing configurations.

The C3's larger frame surface area makes it the most architecturally prominent unit in the self-contained C-Series and provides more surface area for customization and design integration than either the C1 or C2.

The C3 insulation system is structurally identical to the C2 — marine-grade plywood frame, Line-X® 16-mil polyurea exterior shell, extra-thick 316-L stainless tub walls, and aninsulated spa cover with child locksincluded standard. The larger tub volume of the C3 means a greater total mass of water to maintain at temperature, which increases the workload on the chiller system relative to the C1 and C2.

The insulation system's quality is therefore more impactful in the C3 than in smaller units — every degree of thermal loss reduction from the exterior shell and cover directly translates to less chiller workload and more stable temperature maintenance.

The C3 uses the same pool and spa-grade Schedule 40 PVC plumbing in 1"–1.5" diameters, hand-insulated throughout, as the C1 and C2. The larger tub volume requires longer plumbing runs between the tub, chiller, pump, and filter, and the hand insulation on every pipe section is particularly important in the C3 to prevent any thermal pickup across these extended runs.

The accessible mechanical layout and serviceable design philosophy are identical across all three models — a licensed plumber or pool and spa technician can access, service, and replace any component without proprietary tools or factory involvement.

The C3 is BlueCube's most commercially capable self-contained model, built to handle up to 100 plunges per day and sustaining 11–15 plunges per hour at 2–4 minute session lengths, holding water temperature within 4°F of the set point throughout consecutive use.

The C3's larger tub size makes it particularly well-suited for commercial environments serving users of varying heights, or for high-end residential households where multiple family members or guests of different heights will share the unit. The same Commercial Upgrade Package available on the C1 and C2 is available on the C3, adding AOP or chlorine drip sanitation, a commercial skimmer, non-metal tub material options, and full DOH documentation.