R-Cubed Capital Partners
R-Cubed Capital Partners is an early-stage venture firm in Winchester, Massachusetts, led by serial deep-tech entrepreneur Stephen Remondi. It backs hard-science startups across health, simulation and water, and its water exposure is deliberately narrow: as of 2026 R-Cubed has backed one water company, anti-fouling membrane maker ZwitterCo, across two rounds, and has led none.
Compiled by Antoine Walter, (don't) Waste Water, from official filings and direct intelligence in Leviathan.
The take
R-Cubed Capital Partners is, in practice, the investment vehicle of Stephen Remondi, an MIT-trained engineer who spent decades building hard-science companies before writing cheques into them. Remondi co-founded and ran Exa, the simulation-software company spun out of MIT that he took public on NASDAQ in 2012 and sold in 2017, and he later founded the cancer-diagnostics company Xsphera Biosciences. R-Cubed is where that operator's instinct goes hunting for the next deep-technology platform.
R-Cubed Capital Partners treats water as one expression of a broader deep-tech thesis, not a standalone mandate. Its single water position is ZwitterCo, a Massachusetts company whose zwitterionic membranes shrug off the fouling that clogs conventional filters, letting plants reclaim the greasy, protein-heavy industrial wastewater that older membranes choke on. R-Cubed first backed ZwitterCo at its 2021 seed round and came back for the 2022 Series A: two cheques into one company, and a lead role in neither.
R-Cubed Capital Partners' wider book, from the medical-imaging AI of AEYE Health to the epidemic-simulation firm Epistemix, shows where Remondi's conviction really sits: platform technologies with hard science underneath, whatever the sector. I read R-Cubed as a generalist that wandered into water through one strong membrane bet rather than a water specialist, which is why (don't) Waste Water rates its water commitment a One-Off. The open question is whether Remondi's next deep-tech cheque lands back in water, or somewhere else entirely.
Water Commitment Score
Compiled from official filings, third-party records, and direct intelligence from investors and founders, in Leviathan · recomputed monthly · as of Jun 2026.
How they invest
Portfolio · 1 water companies
Invests alongside
Highlighted = profiled on (don't) Waste Water.
Frequently asked
- What does R-Cubed Capital Partners invest in?
- R-Cubed Capital Partners backs early-stage, hard-science startups across health, simulation and water rather than a single sector. In water, R-Cubed has made one investment: ZwitterCo, a Massachusetts company building anti-fouling membranes that recover difficult industrial wastewater. The firm invests at seed and Series A stages.
- Who runs R-Cubed Capital Partners?
- R-Cubed Capital Partners is led by Stephen Remondi, its Managing Director and General Partner. Remondi is a serial deep-tech entrepreneur who took the MIT-spun simulation company Exa public in 2012, later founded the cancer-diagnostics firm Xsphera Biosciences, and sits on ZwitterCo's board.
- Where is R-Cubed Capital Partners based?
- R-Cubed Capital Partners is based in Winchester, Massachusetts, in the United States, and was founded in 2019. It is a small, founder-run venture firm rather than a large institutional fund with multiple offices and a broad investment team.
- How many water deals has R-Cubed Capital Partners done?
- R-Cubed Capital Partners has backed one water company, ZwitterCo, across two funding rounds, its 2021 seed and 2022 Series A, and led neither. That single, repeated commitment earns R-Cubed a One-Off rating on the (don't) Waste Water water-commitment scale as of 2026.
- Is R-Cubed Capital Partners the same as R-Cubed Consulting?
- No. R-Cubed Capital Partners is Stephen Remondi's Winchester, Massachusetts venture firm. R-Cubed Consulting is a separate business and technology consulting company focused on enterprise software, and R Cubed Group is another unrelated firm. Only R-Cubed Capital Partners is the water investor profiled here.