Seaweed Materials: Alginate, Hydrogels, Packaging, Batteries and What Comes Next

By Jayson Byles, forager & chef · September 2026

Seaweed materials are the structural polymers a seaweed builds itself from, taken out and put to work in everything from wound dressings to takeaway boxes and battery electrodes: alginate from brown kelps and wracks, carrageenan and agar from red seaweeds, ulvan from green sea lettuce, plus the cellulose and carbon of the whole plant. They gel, film, bind and swell, which is why they turn up in hydrogels, wound dressings, 3D-bioprinting inks and battery electrodes.

This page is for students, researchers and R&D teams who need the materials science in plain English and want to know where the raw plant comes from. We are a small hand-harvest supplier on the Fife shore, not a chemistry department, so every claim below is tied to a linked source and marked with how far the evidence goes. It sits alongside our hub on the other uses of seaweed, and the second half of the page follows the same materials out of the laboratory: packaging you can buy, textiles, carbon and the buildings and fuel that came before.

What the seaweed polymers actually are

Alginate is a linear chain of two sugar acids, mannuronic acid (M) and guluronic acid (G), arranged in blocks. It is the skeleton of every brown seaweed: on our shore that means sugar kelp, oarweed, the wracks, dabberlocks and sea spaghetti. Industrial alginate comes mostly from Laminaria hyperborea, Ascophyllum, Macrocystis and farmed Laminaria japonica (FAO). The ratio of G to M is the number that matters: G-rich alginates make firmer, more brittle gels, M-rich ones more elastic gels, and the ratio varies with species, season and even the part of the plant.

Carrageenan is a sulphated galactan from red seaweeds, historically from carrageen (Chondrus crispus) and today mostly from farmed Kappaphycus and Eucheuma in the Philippines and Indonesia. Three types are sold. Kappa carries one sulphate group per unit and gels firmly with potassium; iota carries two and gives softer, more flexible gels; lambda carries three and does not gel at all (FAO). Agar, from Gelidium and Gracilaria, is about 70 per cent agarose, the neutral fraction that sets into the firm, clear gel every microbiology plate depends on; it gels between about 28 and 42 °C and does not melt again until 76 to 92 °C (FAO).

Ulvan is the sulphated polysaccharide of green sea lettuce and gutweed (Ulva), built from rhamnose, glucuronic acid, xylose and iduronic acid. It is the newest of the family to interest materials scientists: a 2025 review in Marine Drugs reports ulvan hydrogels swelling to 2,400 per cent of their dry weight and early work on scaffolds and bioinks, all of it still at cell-culture and animal stage (Marine Drugs, 2025).

Cellulose and nanocellulose. Seaweeds contain cellulose alongside their gelling polymers, and from some species it can be broken down to nanofibres or nanocrystals. Cellulose from the green alga Cladophora is over 95 per cent crystalline with a very high surface area, which is why an Uppsala group has used it for battery separators and paper electrodes (Acc. Chem. Res., 2019). Marine Biopolymers in Ayr lists seaweed nanocellulose among the co-products of its alginate process (company site). Seaweed-derived carbon is the whole plant heated without air: the salts and porous structure left behind give a hard carbon with wide, flexible layers, which is what a sodium-ion anode wants (J. Mater. Chem. A, 2017).

A short history, most of it Scottish

Agar came first. Japanese tradition dates its discovery to 1658, when a gel of boiled Gelidium left out overnight froze, thawed and dried into a white sponge that could be reconstituted; the freeze-thaw principle is still used (FAO). In the summer of 1881 Fanny Angelina Hesse, whose husband worked in Robert Koch’s laboratory, suggested agar instead of gelatin for culture media because she had used it to set puddings in hot weather; Koch announced the method the next year (Science History Institute). The same year, on the Clyde at Dalmuir, the chemist E. C. C. Stanford extracted a viscous substance from kelp with alkali and called it algin, the alginate we describe above (FAO).

Scotland then made alginate for 75 years. Cefoil started in Kintyre in 1934; the Ministry of Supply built factories at Girvan, Barcaldine and Kames in 1939, and chromium alginate camouflage netting was a wartime product; the renamed Alginate Industries employed 900 people at Girvan and Barcaldine in 1973; Barcaldine closed in 1996 and manufacture at Girvan ended in 2009, moving to Norway (Grace’s Guide). In 1942 and 1943 Sheina Marshall and A. P. Orr at Millport surveyed the Clyde and the west-coast islands for a British source of agar after Japanese supplies stopped, settling on the red seaweed Gigartina stellata (coast.scot). And in 1973 a Unilever team in Bedfordshire published the egg-box model, still the standard picture of how calcium ions sit between paired G-blocks and turn an alginate solution into a gel (Grant et al., FEBS Letters, 1973). The kelp trade that started all this is on our history page.

How an alginate hydrogel works

A hydrogel is a polymer network that holds a great deal of water without dissolving. Alginate makes one in seconds: drop a sodium alginate solution into calcium chloride and the calcium ions bridge neighbouring G-blocks, the egg-box junctions above, and the liquid becomes a soft, clear solid. That is the whole trick behind alginate wound dressings, the spherification of a restaurant kitchen and most alginate bioinks. A 2025 review in Gels sets out the three routes to a gel, ionic crosslinking with divalent ions, covalent crosslinking and physical crosslinking through hydrogen bonds, and notes that ionic gelation remains the workhorse (Cao et al., 2025).

The same review is frank about the limits. Plain alginate gels are mechanically weak, their breakdown in the body is hard to control because mammals have no enzyme for alginate, cells do not adhere to it unless it is modified with peptides, and batches vary because the plant varies. The fixes are blends with gelatin or chitosan, reinforcement with nanocellulose or graphene oxide, and dynamic crosslinks that let a gel heal itself. The foundational review of the field, Lee and Mooney’s 2012 paper in Progress in Polymer Science, remains the place to start (Lee & Mooney, 2012). Evidence level: alginate dressings and encapsulation are established; the engineered gels are laboratory work.

Bioinks: why alginate is the default and why nobody uses it alone

A bioink is a hydrogel that can be extruded through a nozzle with living cells inside it and hold its shape afterwards. Alginate became the default because it is cheap, cell-friendly and gels instantly in a calcium bath. It is almost never used alone, because cells cannot grip it and the printed structure is too soft. The standard partner is gelatin or its photo-crosslinkable form, GelMA. A 2025 head-to-head found alginate-gelatin gels soft, at 1.5 to 4.5 kPa, and softening with time, while alginate-GelMA gels ran from 6 to 40 kPa and stiffened; stem cells stayed rounded in the first and spread and migrated in the second (2025, open access). A Bergen group reported in February 2025 that as little as 0.1 to 0.5 per cent alginate in a 5 per cent GelMA ink improved printability and more than doubled the compressive modulus, from about 20 to over 50 kPa, while bone-marrow stem cells kept over 90 per cent viability; adding a calcium bath afterwards reduced viability (Scientific Reports, 2025). Evidence level: cell culture. No bioprinted tissue built on these inks is in routine clinical use.

Batteries: binders, separators and the plant as carbon

Alginate’s value in a battery is mechanical. An electrode is a powder held to a foil by a binder, and silicon and hard-carbon powders swell and crack the binders used today. Alginate is stiff, water-processed and carries carboxyl groups that bond to particle surfaces. In April 2023 Marine Biopolymers of Ayr and the University of Glasgow reported a prototype silicon anode bound with Scottish seaweed alginate whose cycle life was two to three times that of graphite electrodes (Envirotec, 2023); a 2026 Advanced Functional Materials paper cross-linked sodium alginate into an interpenetrating network binder for hard-carbon sodium-ion anodes and reported 94 per cent capacity retention over long cycling (Wu et al., 2026). On the separator side, a Bristol-led team made cellulose nanofibres from brown seaweed into a membrane that stopped sodium dendrites puncturing it (Bristol, 2022). And the plant itself, pyrolysed, gives a porous carbon that has been made into a zinc hybrid battery capacitor electrode after activation in plain seawater (J. Energy Storage, 2025). Evidence level for all four: laboratory or prototype cells.

Packaging: the one that is already on sale

Seaweed packaging is the most visible new use because you can hold it. Notpla, whose founders prototyped an edible water pod at Imperial College in 2013, handed out 36,000 seaweed-membrane pods at the 2019 London Marathon and won the Earthshot Prize in 2022 for a material that lines takeaway boxes and replaces plastic film. The company had replaced 21 million single-use plastic items across Europe by June 2025 and says it is aiming for a billion a year by 2030 (Euronews, 2025). In July 2025 the Allianz Stadium in Twickenham put its rugby-ball-shaped drinks carrier into matchday service, after replacing more than 100,000 plastic items with seaweed-lined trays and forks (Allianz Stadium, 2025). Its seaweed comes from France, Spain and South America, not from Britain. Evidence level: commercial product, in use.

In Scotland, Oceanium in Oban has developed a home-compostable seaweed film and board it calls Oceanware, with the Centre for Process Innovation, and raised $2.6 million in 2023 to scale its biorefinery (Packaging Scotland). Evidence level: pilot. The caveat for all of it is scale. The UK produces roughly 15,000 wet tonnes of seaweed a year by hand harvest and cultivation, against 25 to 30 million tonnes farmed worldwide, mostly in Asia (SCI, Nov 2025). A seaweed packaging industry needs a seaweed farming industry behind it.

Textiles: fibre from kelp

Two routes exist. The older one, SeaCell, has been made since 2005 by the German firm Smartfiber: powdered brown seaweed is embedded in a lyocell wood-cellulose fibre, so the seaweed is an additive rather than the fibre itself (Smartfiber). The newer one spins the seaweed polymer directly. Keel Labs’ Kelsun yarn is made by extracting a biopolymer from kelp, combining it with water and additives, and drawing it into filaments; Stella McCartney showed two hand-crocheted Kelsun pieces in her Summer 2024 collection (Stella McCartney). The water-use and compostability figures on that page are the company’s own. Evidence level: small commercial runs; not yet a fibre you find in a high-street garment.

Carbon: the claim to read most carefully

Seaweed grows fast and takes up carbon dioxide as it does. Whether that removes carbon from the atmosphere for long enough to count is a live scientific argument, and we would rather set it out than pick a side.

• A 2025 modelling study in Communications Sustainability found that organic matter falling from seaweed farms raises the alkalinity of the sediment below, a route to lasting carbon storage, and estimated an average of about 0.85 tonnes of CO₂ removed per hectare per year, with a range of 0.1 to 2 (Nature, 2025). Evidence level: model, not measurement.
• A 2022 paper in the ICES Journal of Marine Science argued that seaweed ecosystems may not mitigate CO₂ emissions at all once you account for what the animals living in them respire (Gallagher et al., 2022); it drew published rebuttals.
• A 2024 review in the Journal of Phycology by Catriona Hurd and colleagues concluded that verifying seaweed carbon removal is hard because the sea does not re-equilibrate with the air quickly, so carbon fixed by seaweed may not draw more CO₂ out of the atmosphere (Hurd et al., 2024).

Our position is plain. The seaweed we cut is a food and a raw material. We do not sell it as an offset and we do not believe anyone should yet.

Fuel: the idea that came before the others

Seaweed fuel had its moment before packaging did, and Scotland led it. BioMara, a €6 million programme led from the Scottish Association for Marine Science in Oban and funded largely by the EU’s Interreg IVA scheme, tested seaweed and microalgae as biofuel feedstocks from 2009 to 2013 with partners in Northern Ireland and the Republic (SAMS). MacroFuels followed, a €6 million Horizon 2020 project from 2016 to 2019 in which SAMS grew the seaweed and Danish and Dutch partners fermented it to ethanol, butanol and biogas; the project took the technology from readiness level 3 to 4 or 5 (CORDIS). Evidence level: pilot. No commercial seaweed fuel followed in Britain. What did follow was the cultivation know-how: SAMS now runs two research seaweed farms and a nursery that supplies growers (coast.scot). Fuel is the lowest-value thing you can make from a kilogram of seaweed, and the sector learned to sell the polymers first.

Buildings: roofs, boards and foams

The oldest seaweed building material is not, strictly, a seaweed. From the 1660s the women of Læsø, off Denmark, thatched roofs with eelgrass, a flowering seagrass, and some of those roofs still stand; the Danish firm Søuld now presses eelgrass into acoustic and insulation panels (Søuld). Evidence level: product on sale, niche. For true seaweeds the work is younger. A 2024 study pressed washed-up seagrass into boards with a thermal conductivity of 0.047 W/m·K, in the range of polystyrene (ScienceDirect, 2024); another made binderless particleboard from brown Sargassum by heat and pressure alone (PMC, 2024); and alginate has been foamed with cellulose nanofibres into an insulating aerogel (PMC, 2021). Evidence level: laboratory samples.

What changed in the UK in 2025 and 2026

The structure around all this is finally being built. In June 2025 Cefas published guidance on marine licences for seaweed farms, the bottleneck growers had complained about (SCI). In November 2025 a representative body, UK Seaweed, was launched at the Scottish Seaweed Industry Conference in Oban after an 18-month consultation by the UK Agri-Tech Centre, with Seaweed Scotland as secretariat and funding from WWF-UK (UK Agri-Tech Centre). On 6 January 2026 the UK Seaweed Network was launched in Parliament, led from UCL Biochemical Engineering with Seaweed Scotland, the UK Agri-Tech Centre, WWF-UK and the Fishmongers’ Company, to join up research, scale-up and policy across the four nations (UCL). The Scottish Government’s 2022 baseline put the sector here at about £4 million and 59 jobs (gov.scot), so the room to grow is obvious. So is the constraint: in 2018 the Scottish Parliament banned mechanical dredging of kelp after a company proposed taking 30,000 tonnes a year from the west coast (Scottish Wildlife Trust). Whatever the future of seaweed is here, it will be cut, farmed, or both, and not dredged.

What the research says now

Five developments from the last three years that a reading list should include, each with its evidence level:

• 2023, Glasgow and Ayr. Seaweed alginate binder for silicon anodes, watch-battery prototype, IBioIC-funded; commercial timeline given as three to five years (Envirotec). Prototype.
• January 2025, ulvan review. Composition, extraction yields and biomaterial uses of ulvan from Ulva, with bioink work flagged as promising and preclinical (Marine Drugs). Cells and animals.
• February 2025, Bergen. Low-alginate GelMA bioinks print large structures without a calcium bath (Scientific Reports). Cell culture.
• 2025, alginate hydrogel review. Crosslinking routes, smart-responsive gels and the unsolved problems of strength, degradation and batch variability (Gels). Review of lab and preclinical work.
• 2026, sodium-ion binder. Cross-linked alginate binder, 94 per cent retention in hard-carbon anodes (Advanced Functional Materials). Laboratory cells.

Sourcing raw material for a lab or a start-up

If you need tonnes of alginate you buy it: Scotland has not made it since Girvan closed, and industrial supply comes from Norway, Iceland and China (gov.scot). If you need the plant, to extract your own polymer, characterise a species, or test a whole-biomass route such as carbon or particleboard, the questions are different, and they are the ones we can help with.

• Species decides the polymer. Alginate and fucoidan come only from browns, carrageenan from carrageen, ulvan from Ulva. Ask for one species, named in Latin, and a single-species batch.
• Season decides the yield. Polysaccharide content and composition shift through the year; a 2022 study of Laminaria hyperborea tissues and the co-products of alginate extraction found metabolite profiles that differed by harvest season (J. Appl. Phycol.). Say what you want it for and we will say when to cut it; our year on the shore gives the calendar.
• Handling decides the chemistry. Rinsed in clean seawater, chilled within hours, dried low. High heat and long soaking change what you extract.
• The law decides the scale. Anything beyond personal use on Crown foreshore needs a licence from Crown Estate Scotland, and since November 2018 mechanical dredging of kelp is banned in Scotland (Scottish Wildlife Trust). Wild harvest here is roughly 8,000 tonnes a year, cut by hand. Our guide to the law covers the rest.

We supply hand-cut, identified Scottish seaweed from the Fife shore in the small quantities a bench needs, fresh or dried, with the shore and date on every bag; the forms, species and quantities are on the commercial supply page. We do not cut Laminaria hyperborea, which grows below the tide; our kelps are sugar kelp and oarweed. For the clinical uses these materials already have, see seaweed in medicine.

Sources

• Algin, a brown seaweed polysaccharide (FAO)
• Production, properties and uses of carrageenan (FAO)
• Agar, a red seaweed polysaccharide (FAO)
• Ulva seaweed-derived ulvan: a promising marine polysaccharide for biomaterial design (Marine Drugs, 2025)
• Cladophora cellulose: unique biopolymer nanofibrils for energy, environmental and life science applications (Accounts of Chemical Research, 2019)
• Marine Biopolymers Ltd, Ayr (company site)
• Kelp-derived hard carbons as anode materials for sodium-ion batteries (Journal of Materials Chemistry A, 2017)
• Fanny Angelina Hesse (Science History Institute)
• The history of alginate extraction, by Jim Bailey (Grace’s Guide)
• Seaweed at SAMS in wartime and today (coast.scot)
• Biological interactions between polysaccharides and divalent cations: the egg-box model (FEBS Letters, 1973)
• Research progress of sodium alginate-based hydrogels in biomedical engineering (Gels, 2025)
• Alginate: properties and biomedical applications (Progress in Polymer Science, 2012)
• Gelatin vs GelMA in alginate-based bioinks as a platform for 3D-bioprintable in vitro systems (2025)
• Bioprinting of mesenchymal stem cells in low-concentration GelMA/alginate blends without ionic crosslinking (Scientific Reports, 2025)
• Scottish seaweed sparks idea to boost electric vehicle batteries (Envirotec, 2023)
• Crosslinked sodium alginate binder for long-life hard carbon anodes in sodium-ion batteries (Advanced Functional Materials, 2026)
• Seaweed-based battery powers confidence in sustainable energy storage (University of Bristol, 2022)
• Seawater activation of a seaweed-based porous carbon for a zinc hybrid battery capacitor (Journal of Energy Storage, 2025)
• Status of the current seaweed-based industry in Scotland (Scottish Government, 2022)
• Tissues and co-products from alginate extraction of Laminaria hyperborea show metabolite profiles that depend on harvest season (Journal of Applied Phycology, 2022)
• Licensing of wild seaweed harvesting (Crown Estate Scotland)
• Unsustainable kelp dredging banned in Scotland (Scottish Wildlife Trust, 2018)
• Notpla, Earthshot Prize winner 2022 (The Earthshot Prize)
• Seaweed is taking plastic out of stadiums and sandwich boxes (Euronews, June 2025)
• Allianz Stadium serves up UK-first plastic-free drinks carrier (Allianz Stadium Twickenham, July 2025)
• Developing premium compostable bio-packaging from seaweed: Oceanium (Centre for Process Innovation)
• Oban-based Oceanium secures $2.6 million (Packaging Scotland, 2023)
• Seaweed’s remarkable future: new materials and new science (SCI Chemistry & Industry, November 2025)
• SeaCell fibre (Smartfiber AG)
• Keel Labs Kelsun seaweed fabric (Stella McCartney, 2024)
• Seaweed farms enhance alkalinity production and carbon capture (Communications Sustainability, 2025)
• Seaweed ecosystems may not mitigate CO2 emissions (ICES Journal of Marine Science, 2022)
• Air-sea carbon dioxide equilibrium: will it be possible to use seaweeds for carbon removal offsets? (Journal of Phycology, 2024)
• Celebrating BioMara (Scottish Association for Marine Science, 2012)
• MacroFuels: developing the next generation macro-algae based biofuels (CORDIS, European Commission, 2016 to 2019)
• Eelgrass as a building material (Søuld)
• Seaweed boards as value-added natural waste product for insulation and building materials (2024)
• Development of a binderless particleboard from brown seaweed Sargassum spp. (2024)
• Seaweed-derived alginate and cellulose nanofibre aerogel for insulation applications (2021)
• UK Seaweed launch unlocks new growth opportunities (UK Agri-Tech Centre, November 2025)
• Network launched to unlock potential of seaweed in the UK (UCL, January 2026)
• Understanding the potential scale for seaweed-based industries in Scotland (Scottish Government, 2022)

Questions we get asked

What is seaweed packaging made from?

Mostly alginate, the gelling polymer of brown kelps and wracks, sometimes with carrageenan from red seaweeds. Notpla’s films and box linings, and Oceanium’s Oceanware in Oban, are seaweed polymers cast as coatings or sheets. They compost in weeks because the polymer is left much as the plant made it.

Can seaweed really be used in batteries?

In parts of them, yes, at laboratory stage. Seaweed cellulose nanofibres have made a separator that stops sodium-metal cells short-circuiting, and alginate has been used as the binder holding silicon and hard-carbon anodes together, including in a Scottish prototype from Marine Biopolymers and the University of Glasgow. No commercial battery uses them yet.

How does alginate form a hydrogel?

Alginate is a chain of mannuronic (M) and guluronic (G) acid blocks. When calcium ions meet the G-blocks they sit between paired chains like eggs in a box, cross-linking them into a network that traps water. The gel forms in seconds in a calcium chloride bath; G-rich alginates give firmer gels, M-rich ones more elastic gels.

What is the difference between agar, carrageenan and alginate?

Agar and carrageenan come from red seaweeds and are galactose polymers; alginate comes from brown seaweeds and is a uronic-acid polymer. Agar sets on cooling and melts on heating. Carrageenan gels with potassium or calcium depending on type. Alginate gels with calcium at any temperature and does not melt, which is why it suits dressings and bioinks.

Does seaweed farming capture carbon?

Seaweed takes up carbon dioxide as it grows, but whether farms remove carbon from the atmosphere for the long term is contested. A 2025 model put it at about 0.85 tonnes of CO₂ per hectare per year; other researchers argue slow air-sea exchange and respiration by the animals living in seaweed mean the net effect may be small.

Stages and figures on this page were checked in September 2026 against the sources listed and will be revised as results are published. It describes materials and published research, not medical products or advice. Extracts intended for food, medical or cosmetic use are subject to their own authorisations; talk to the relevant regulator before you launch.