Technical note 17

TN-17: Leather: the Cover, the Hide, and the Source

What goes on the outside of an upholstered seat meant to be renewed on a fifteen-to-thirty-year cycle: the cushion stack under the cover, leather against synthetic covers, what a hide costs in environmental and moral terms, and where a traceable hide can come from, and how the covered panel bolts to the oak without clamping the cover. Written for the thousand-year build, the Keel Truss lounge with upholstered seat and back panels. First draft 25 September 2026; joint, cartridge and cushion-section sections added the same day. Status: DRAFT. Web sources were read on 25 Sep 2026 and are marked VERIFIED where the claim was checked against the page; the durability comparison is STANDARD materials behavior with no head-to-head study found; the kangaroo cutting geometry is DERIVED; several practical claims are UNVERIFIED and are flagged where they appear.

The claim

For a cover that must reach its next re-upholstery in good condition, a full-grain, vegetable-tanned hide from a named source is the strongest choice, with heavy wool or mohair as the non-animal alternative. Polyurethane imitation leather and bonded leather are unlikely to last one cycle. The environmental and moral cost of a hide is small at the margin, because a hide carries a few percent of an animal's economic value, and in some recent years the marginal hide went to landfill. The argument that remains is complicity, which no arithmetic answers; the defensible response is provenance, a hide whose ranch, harvest, and tannery can be written into the document that rides inside the cushion.

Under the cover: the stack

Good upholstery is a stack, and each layer has one job. From the frame outward: a suspension (springs, webbing, or a rigid deck), a support core, a softer comfort layer or a zoned core, a wrap, and the cover. The thousand-year lounge uses a rigid plywood deck, so its give has to come from the stack above the panel. TN-16 set out the soft-over-firm principle for the Keel Chair's thin seat; the lounge applies the same principle at 125 mm of seat and 90 mm of back.

Polyurethane foam displaced the older materials after about 1957. An industry history from the molded-foam trade traces the sequence: coil springs with horsehair and other natural stuffing, then latex-bonded hair from the 1930s into the 1960s, then latex foam, then polyurethane, with high-resilience (HR) foam developed in the 1970s to recover latex's feel. The same document notes that molded cushions can be made firmer in the bolsters than in the seating area within one pad, which is how a firmer front edge is built [VERIFIED, Molded Polyurethane Foam Industry Panel, 2008]. The Polyurethane Foam Association defines the three numbers that specify a foam: density (mass per volume; higher density retains its properties longer), indentation force deflection (IFD, the force to push a 50 square inch indentor 25 percent into a 4 inch sample), and support factor (65 percent IFD over 25 percent IFD, typically 1.5 to 2.6; low values bottom out) [VERIFIED, PFA glossary and foam-performance pages]. The PFA pages give no recommended values for seats; the grade is chosen with the upholsterer and then measured.

The Eames Lounge Chair shows the drift in practice. Herman Miller says only that its cushions are individually upholstered and replaceable [VERIFIED]. A conservation firm that restores the 670 and 671 gives the history: soft leather over down and feathers at introduction, foam added to the down in 1960, and foam with Dacron polyester wrap in current production [VERIFIED as that firm's account]. For cinema recliners no primary manufacturer specification was found; one seating maker describes its standard multiplex chair as using high-density cold-cured molded foam [VERIFIED as that maker's claim]. What springs, if any, sit under luxury recliners is UNVERIFIED.

The proposed stack for the lounge seat is a firm HR base, a softer HR comfort layer, a firmer strip at the front edge, and a Dacron or down-and-feather wrap; the back is a single HR layer carrying laminated lumbar and head pads, wrapped. A thin pocketed-coil unit bonded to the ply in place of part of the base foam would restore some of the compliance a rigid deck gives up. The front strip matters to the geometry: the layout assumes the seat foam compresses to 85 mm under the sit bones and 110 mm at the front edge, which is what turns a 12 degree loaded seat into an 8.9 degree hard pan. Those two numbers are assumptions until the chosen stack is measured on a board tilted to 9 degrees.

The cushion sections

The proposed sections, constant across the width, are drawn at 1:1 in 1000-year-build/thousand-year-lounge-cushion-sections.svg. The seat carries 125 mm over 12 mm ply: a 12 mm closed-cell base, 65 mm firm HR, 38 mm soft HR over the rear 400 mm with a 100 mm firm HR strip at the front, a 25 mm firm HR nose over the ply edge at radius 50, and a 10 mm polyester wrap. The back carries 90 mm: 12 mm closed-cell, 50 mm medium HR, 20 mm soft HR and an 8 mm wrap, with a medium HR lumbar pad 30 mm proud at 217 to 317 mm along the back from the hard corner and a head roll 65 mm proud at 707 to 967 mm, both laminated under the wrap so the ply stays flat. The back cushion starts 150 mm up the back plane and clears the seat's free top by 7 mm at the ply and 43 mm at its face. These are proposals [DERIVED]; foam grades are chosen with the upholsterer and checked on the tilted board.

Leather against synthetic covers

No peer-reviewed study comparing the service life of leather and synthetic upholstery covers was found; the available comparisons are vendor pages. The comparison therefore rests on failure mechanisms, which are STANDARD. Full-grain and aniline leather is a fibre network with no applied film to lose; it fails by drying, cracking at creases, and light fade, all slowed by conditioning and shade, and it can be cleaned, re-oiled, re-dyed and patched. Corrected or pigmented top-grain carries a coating that resists stains and is harder to repair invisibly once it cracks. Bonded leather, shredded fibre on a backing under a polyurethane face, is the weakest option. Polyurethane imitation leather fails by hydrolysis of the polymer and by delamination of the face film, which cannot be repaired. PVC vinyl outlasts polyurethane but stiffens and cracks as plasticizer migrates, and it breathes poorly. Woven covers can be very durable: solution-dyed acrylic, nylon, polyester, wool and wool mohair are rated by Martindale and Wyzenbeek abrasion tests, and contract grades run well past residential need. They end their lives by pilling, seam fray, fade and unremovable stains more often than by abrasion. That leather cushions of the 1950s and 1960s are routinely reconditioned rather than replaced is UNVERIFIED as a general claim, though it is the restorers' premise.

For the renewal cycle this gives two workable covers, full-grain semi-aniline leather and a heavy wool or mohair weave, and rules out polyurethane imitation leather and bonded leather. Leather also tolerates removal and re-stretching if a cover must come off between cycles.

What a hide costs

A slaughtered animal yields meat, a hide and other co-products at once, and a life-cycle assessment must decide how much of the farm-to-slaughter burden the hide carries. Treating the hide as a by-product assigns it nothing, the tanners' preferred view. Allocation by mass assigns its share of live weight; allocation by economic value assigns its share of revenue. A 2025 study of Italian beef supply chains found hides at about 5.9 percent of live weight and 2.7 percent of economic value in 2023, gives upstream footprints for raw hide of 1.63 kg CO2e per kg under economic allocation and 3.55 under physical allocation, and argues for economic allocation [VERIFIED, Lunesu et al. 2025].

Economic allocation is also the answer to the causal question a buyer asks. Cattle are raised for total revenue per animal; a lasting rise in demand for leather raises hide prices, adds slightly to the value of each animal, and draws out slightly more cattle, in proportion to the hide's share of value. The market has recently made that share smaller. Hide values fell sharply from 2018, native hides brought about US$29 to $30 in late August 2020 against about $120 five years earlier, and the Leather and Hide Council of America reported that about 5.5 million US hides, nearly 16 percent of production, failed to reach the leather chain in 2019, most of them landfilled [VERIFIED, Canadian Cattlemen reporting LHCA figures]. Where some hides are being discarded, a marginal purchase diverts a hide from landfill more than it adds an animal. The environmental weight of leather then sits mainly in the tannery, especially chrome tanning, which is one reason vegetable tanning is the usual choice where this is weighed [the tannery comparison is UNVERIFIED here and needs its own source].

What the philosophers say

Moral philosophy treats the question as a case of the inefficacy, or no-difference, problem. Shelly Kagan argues that even where a single purchase seems to change nothing, supply chains have thresholds, and a small chance of triggering a large production step has the same expected effect as a proportional share of it [VERIFIED, Kagan 2011]. Mark Budolfson replies that real supply chains contain slack, waste and buffering, so the expected effect of a marginal purchase can fall well below proportional [VERIFIED, Budolfson 2019]. Gesang and Ullrich press the same point against Kagan's symmetry assumption using subsidized EU agriculture [VERIFIED, Gesang and Ullrich 2020]. Views that do not rest on consequences hold that using the products of a harmful practice is complicity or endorsement whatever the causal effect; on those views the few percent of value does not settle anything, and the choice of source becomes the whole of the answer.

Where a hide can come from

Welfare certification is common for beef and rare for leather, because hides are pooled at the packing plant. The Leather Working Group audits tanneries on environmental performance. Textile Exchange's Leather Impact Accelerator and WWF's traceability guidance aim at deforestation-free chains traced to the farm; which welfare frameworks the Accelerator requires was not confirmed, because its detailed documents could not be read [UNVERIFIED]. Label claims are fragile. Belcampo Meat Co., sold on its own ranch sourcing, was shown in 2021 to have sold meat from other producers under its label; the company admitted it, USDA inspectors cited its plant, and the board closed the business in October 2021 [VERIFIED, press coverage]. The dependable route for one chair is to leave the commodity chain: hides bought from a named pasture or welfare-certified ranch and custom tanned, which small tanneries do routinely for ranchers and hunters [UNVERIFIED as a survey of tanneries; common practice].

Bison leather is readily available and comes from ranched animals. The National Bison Association reports 192,477 bison on 1,986 private US ranches and farms in the 2022 USDA census, about 11,000 in federal herds, 10,000 in state and other public herds, about 30,000 on tribal lands in the US and Canada, and around 80,000 US bison harvested in 2023 [VERIFIED]. The hide is a by-product of bison meat. How individual ranches finish their animals is not in those figures and has to be asked. Horween's Montana Bison is one tannery line on the market [VERIFIED as listed by a distributor].

Wild Idea Buffalo Co. of Hermosa, South Dakota, the ranch of Dan and Jill O'Brien and the subject of Dan O'Brien's Wild Idea: Buffalo and Family in a Difficult Land (University of Nebraska Press, 2014), harvests in the field: the animal is shot on pasture and skinned in a mobile unit under a USDA inspector, and the hide is laid out on the prairie and salted. The company says its hides are vegetable tanned and used by Moore & Giles, Patagonia and Tecovas for boots, bags and small leather goods; skulls are cleaned and sold or donated to local Native American communities [VERIFIED, company pages and Agweek]. The Moore & Giles collection uses full-grain hides vegetable tanned at Hermann Oak Leather in St. Louis and suede from Pergamena in the Hudson Valley, and it offers bags and small goods, with no upholstery leather listed [VERIFIED]. Moore & Giles also supplies furniture leather through a separate business, which makes it the natural first enquiry about bison finished for upholstery; Hermann Oak is known for firm harness and saddle temper, and whether a supple upholstery temper is available is UNVERIFIED.

Kangaroo is the one large wild-harvested source. The animals are wild, taken under state quotas approved and published by the federal environment department, and a national code of practice requires head shots and the killing of dependent young, which is the principal welfare objection [VERIFIED for the quota system; the code's provisions per a secondary summary]. Deer and elk hides from regulated hunting are tanned to order and are soft and small. No regular commercial supply of leather from wild bison culls was found.

The kangaroo rectangle

An importer describes kangaroo skins as roughly triangular, about 3 feet (915 mm) on each side, 3 to 9 square feet and averaging 5 to 6 (0.46 to 0.56 square metres), 0.6 to 1.4 mm thick, with a top grade defined by a clean central triangle 3.5 feet on a side and most supply in the middle grades [VERIFIED, PanAm Leathers]. The largest rectangle inscribed in a triangle takes half its area, half the base wide and half the height tall; for an equilateral triangle of side s that is s/2 by 0.433s, or 457 by 396 mm at s = 915 and 533 by 462 mm at s = 1067 [DERIVED]. Allowing 25 to 50 mm off each side for thin belly and leg edges and for scars gives about 400 by 350 mm from a typical skin [DERIVED from an UNVERIFIED trim allowance]. A lounge seat top of about 550 mm square is beyond one skin, so a kangaroo cover would be a patchwork, which is compatible with the mosaic character of the scrap chairs.

Bolting through the cover

The lounge's seat and back panels are upholstered on both faces, and each bolts to the oak through its covered back face at four stations, an M6 bolt into a T-nut set from the foam side of the 12 mm ply. Trade practice in office-chair seat pans and contract seating is to staple the cover, locate each T-nut by feel or by a template taken from the panel edges, pierce the cover (a 4 to 5 mm punch in leather, a hot awl in synthetic weaves), and drive the bolt through [UNVERIFIED as a survey; common practice]. Two-part brass grommets (a #0 grommet has a hole of about 6.4 mm) give a finished, reinforced hole, but their back flange sits between cover and ply and wants a shallow counterbore, and they must be set in the cover before it is fitted. Both details clamp the stick against leather or cloth, and a compliant layer under a bolt keeps creeping, the slackening mechanism of TN-7. The joint below takes the cover out of the clamp entirely.

A flanged bronze sleeve runs through the full thickness of the oak stick, with the bolt head and washer on its outer flange. Its inner end stands proud of the stick face by the cover thickness plus a clearance, passes through a hole punched in the cover at least as large as the sleeve, and lands on bare ply. The T-nut goes in from the foam side with its barrel stopping just short of the back face of the ply, by a recess δ. Tightening compresses the ply under the sleeve until the sleeve lands on the barrel end; from then on further preload passes sleeve to barrel, metal to metal. The ply is held at a squeeze fixed by δ and not by the bolt torque. This is KU's detail (25 Sep 2026) and it is the compression-limiter arrangement used where bolts clamp plastic parts [STANDARD engineering practice]. It improves on an earlier proposal in the same session, which put the ply in the preload path.

The load paths separate cleanly. Bolt preload runs bolt head, sleeve, barrel end, T-nut thread, all metal, so it does not relax as wood creeps or moves with humidity. The ply's clamp is set by δ and reacted by the T-nut flange. Shear from the panel, which is the member that ties the two side frames, goes from the ply into the barrel in bearing, from the barrel into the sleeve by friction under full preload, and from the sleeve into the oak in bearing. The oak carries no clamp at all; it locates the sleeve in a plain bore.

Four details make it work. First, δ is small and must be machined against the measured sheet: the ply's squeeze is roughly its through-thickness stiffness times δ over 12 mm, and if that stiffness is a few hundred MPa, which is an UNVERIFIED estimate, δ is nearer 0.1 to 0.15 mm than 0.5. That is finer than the sheet-to-sheet variation of Baltic birch, so δ is set by counterboring the flange into the foam face to depth or by facing the barrel after installation, and checked on a coupon with a feeler gauge. Second, the sleeve bore must be smaller than the barrel's outside diameter so the sleeve lands on the barrel. With a 6.5 mm bore on an 8 mm barrel the contact ring is about 17 mm², about 175 MPa at an assumed 3 kN preload, adequate in steel and marginal in bronze; a barrel of 10 to 12 mm multiplies the contact area several times [DERIVED]. Third, stamped T-nuts often have rounded barrel ends and thin formed barrels not meant for axial load; a turned flanged nut with a thick barrel and a faced end is the right part. Fourth, the barrel is the shear key, so the ply is drilled for a close fit and the barrel bedded in epoxy. For the stage before the sleeve lands, a 25 mm sleeve over an 8 mm hole puts roughly 7 MPa on the ply at 3 kN, while an 18 mm sleeve about doubles that [DERIVED; the crushing strength of birch ply through its thickness, taken here as on the order of 10 MPa, is UNVERIFIED].

The panel is a cartridge

The ply panel and its T-nuts are expected to last about a century, several re-upholstery cycles, and then be replaced together. The joint is arranged so that nothing permanent is threaded. The oak and the sleeves carry plain bores; the thread lives in the nut and the bolt, which are replaced with the panel, so the survival of the M6 standard does not matter. A future maker drills a new panel and uses whatever nut and bolt fit a 6.5 mm sleeve bore, the principle of four plain holes in the oak set down on 17 September. The T-nut therefore can be an ordinary turned stainless or brass part. The sleeves are the long-lived hardware: they fix the stick-to-panel gap for every future cover and the bearing the oak sees, so they are turned in bronze, faced square, and sized for indefinite reuse, and their outer flanges are a place for the maker and restorer ciphers of TN-11.

The document inside the cushion should specify the interface, not the panel: the station positions relative to the sticks, the sleeve bearing diameter, δ and how to measure it, and the shear stiffness a replacement panel must supply. That lets a future upholsterer make one from whatever shear panel exists. The likely end of a ply panel is its glue lines, the panel problem of TN-1, and before that its nuts may loosen in their bores. A little looseness is tolerable in a part scheduled for replacement, and the recess keeps a worn panel from being crushed while it waits.

Open questions

The compressed thickness of the chosen stack at the sit bones and the front edge, measured, to replace the 85 and 110 mm assumptions. Whether Moore & Giles or Hermann Oak will finish Wild Idea bison at an upholstery temper, and at what thickness. A sourced comparison of chrome and vegetable tanning impacts. The Leather Impact Accelerator's welfare requirements. A citable source for the reconditioning life of mid-century leather cushions. The through-thickness stiffness and crushing strength of Baltic birch ply, to fix δ from a number rather than a coupon, and the coupon test itself. The sleeve and nut drawings, once the cleat stations are fixed.

Sources

All read 25 Sep 2026; journal metadata checked against Crossref. Lunesu, M.F., Correddu, F., Carta, S., Sechi, S., Farina, M., Pulina, G. (2025). Attributing farm-to-slaughter emissions to hides: evidence from beef supply chains. Animals 15(24), 3546, doi:10.3390/ani15243546. Kagan, S. (2011). Do I make a difference? Philosophy & Public Affairs 39(2), 105-141, doi:10.1111/j.1088-4963.2011.01203.x. Budolfson, M.B. (2019). The inefficacy objection to consequentialism and the problem with the expected consequences response. Philosophical Studies 176(7), 1711-1724, doi:10.1007/s11098-018-1087-6. Gesang, B., Ullrich, R. (2020). To buy or not to buy? The moral relevance of the individual demand in everyday purchase situations. Food Ethics 5, article 12, doi:10.1007/s41055-020-00069-2. Molded Polyurethane Foam Industry Panel (2008), Automotive Cushioning Through the Ages, moldedfoam-ip.com. Polyurethane Foam Association, Glossary and Foam Performance, pfa.org. Herman Miller, Eames Lounge and Ottoman product details, hermanmiller.com. Conservation & Design International, Eames Lounge Chair Set (670/671) Restoration, bernackiconservation.com. Leadcom Seating, cinema seating guide, leadcomseating.com. Canadian Cattlemen, Cattle hides take a tanning, canadiancattlemen.ca (LHCA figures). Leather International, Staggering decline in hide share of cattle value, leathermag.com. Wikipedia and LAist on Belcampo's 2021 closure. Textile Exchange, Leather Impact Accelerator; WWF, deforestation-free leather traceability guide. National Bison Association, Bison by the Numbers, nationalbison.org. The Tannery Row, Horween Montana Bison. Wild Idea Buffalo Co., FAQ and Humane Field Harvest pages, wildideabuffalo.com; Agweek, Respect in life, dignity in death. Moore & Giles, Moore & Giles x Wild Idea: Bison Leather Collection, mooreandgiles.com. University of Nebraska Press, Wild Idea (9780803250963). DCCEEW, commercial kangaroo harvest quotas, dcceew.gov.au; Wikipedia, Kangaroo industry (secondary). PanAm Leathers, Understanding and Using Kangaroo Leather; LeatherSkins.com, kangaroo hides.

The Hundred-Year Chair · hundredyearchair.com · technical notes, public from first draft. home · the technical notes · the book