Obeche — Density, Movement, Workability & Cost

Obeche (Triplochiton scleroxylon) is lighter than western redcedar, which is a genuinely unusual claim for a tropical hardwood to make — most tropical species run dense and heavy, and obeche's featherweight character is exactly why it dominates two very specific, very different markets: sauna benches and model aircraft.

An oddity among tropical hardwoods

At 23.8 lb/ft³ and 440 lbf on the Janka scale, obeche is soft, woolly, and startlingly light for a tree grown in West and Central Africa's tropical forests. It needs genuinely sharp tools to avoid fuzzing, the same working caution basswood and aspen demand, and it will not hold a screw under real load — a project depending on obeche for structural fastening strength is asking more of the wood than it can reliably give.

Modest movement, in keeping with its light overall character

Radial shrinkage of 3% against a tangential figure of 5.4% gives a 1.8 ratio, reasonably contained, which is part of why a wide obeche model-aircraft sheet stays flat as a shop's humidity swings through a season. A 10"-wide board loses only about 0.108" (2.7mm) across its width moving from a 12% moisture content down to a dry 6%; a different sheet width runs through the wood movement calculator. Milled 1" thick and 6 feet long at that same width, the board weighs about 9.9 lb at obeche's very light milled density — the wood weight calculator covers other board sizes.

Gluing greedy end grain, and a finish that goes either way

Gluing is fine, though the end grain drinks adhesive fast enough that a thinned sizing pass first is genuinely worth the extra minute rather than risking a starved joint. It paints and dyes evenly, and a clear finish leaves it looking essentially unfinished — a plain, pale surface without much figure to show off, which is fine for a sauna bench and beside the point for a model aircraft skin anyway.

Durability, cost, and a documented occupational hazard

Obeche is non-durable and highly susceptible to insect attack, ruling out any exterior or ground-contact use regardless of price. It prices out at roughly $8 a board foot — this site's moderate tier — cheap for an imported hardwood given its light weight and easy machining. Sauna benches, model aircraft, veneer core stock, mouldings, and pattern making round out its markets. The dust is a documented occupational asthma agent — one of the better-studied wood-dust sensitisers in European sawmilling literature, which is worth knowing given how mild and unthreatening the wood otherwise feels to work.

Why sauna builders specifically choose it

Obeche shares with quaking aspen and northern white cedar the specific property that matters for a sauna bench: low thermal mass, so it doesn't retain heat against bare skin the way a denser wood would. Where those two are domestic options, obeche is the tropical import version of the same idea, chosen where regional availability or a specific supply chain favours it.

What people actually ask about obeche

Does obeche's low weight give it a strength-to-weight advantage the way it does for a genuinely engineered material like Sitka spruce? No — obeche's appeal for model aircraft is purely about absolute lightness for a given size, not an especially favourable strength-to-weight ratio, whereas Sitka spruce is specifically graded and selected because it packs unusual strength into that light weight, a distinction that matters if a project actually needs load-bearing performance rather than just a light, easily-shaped material.

Why does obeche need sharper tools than a similarly soft domestic wood? Its woolly fibre structure fuzzes readily under a dull edge, much like basswood or aspen — a genuinely sharp blade shears the fibres cleanly, while a dull one lifts and tears them, producing a rough, fuzzy surface that sanding alone won't fully correct.

Does obeche's asthma risk apply mainly to industrial sawmill workers cutting large volumes, or should an occasional hobbyist worry too? The documented cases concentrate heavily in sustained industrial exposure rather than occasional hobby use, so a weekend woodworker's realistic risk is considerably lower — reasonable ventilation and a basic dust mask are still sensible, but this isn't a species that calls for the same level of precaution a hobbyist would need with cocobolo or western redcedar.

Obeche's shrinkage numbers are Table 4-4 of the USDA Forest Products Laboratory's Wood Handbook (FPL-GTR-190, 2010); The Wood Database's own 12%-moisture-content testing is the source for density and Janka hardness. It's also among the fastest-growing tropical hardwoods in commercial use, reaching harvestable size in a fraction of the decades a slower tropical species like true mahogany needs — part of why it stays inexpensive relative to its imported status.