Redwood vs Douglas-fir

Redwood and Douglas-fir are the West Coast’s two big softwoods. Douglas-fir is much harder, heavier and stiffer; redwood moves less and its old-growth heartwood resists decay.

Coast Douglas-fir is about 48% harder than old-growth redwood.
Coast Douglas-fir is about 20% heavier than old-growth redwood.
Coast Douglas-fir has about 30% more movement across a flatsawn board than old-growth redwood.

Each column is the species its page leads with: old-growth redwood for redwood, coast Douglas-fir for Douglas-fir.

Side by side

Property	Redwood	Douglas-fir
Janka hardness, 12% MC	480 lbf	710 lbf
Weight, 12% MC	28 lb/ft³ (448 kg/m³)	33.6 lb/ft³ (538 kg/m³)
Specific gravity, 12% MC	0.40	0.48
Tangential shrinkage	4.4%	7.6%
Radial shrinkage	2.6%	4.8%
12 in flatsawn board, 6% → 12% MC	0.148 in	0.192 in
12 in quartersawn board, 6% → 12% MC	0.086 in	0.119 in
Bending strength (MOR), 12% MC	10,000 psi	12,400 psi
Stiffness (MOE), 12% MC	1.34 million psi	1.95 million psi
Crushing strength, 12% MC	6,150 psi	7,230 psi

One source: USDA Forest Products Laboratory, the authority for species properties it measured

Wood Handbook Tables 5-3b, 4-3 and 13-5; weight and movement worked with its Eqs. 4-14 and 13-3. A dash means the Handbook prints no value.

What sets them apart

Decay: Old-growth redwood heartwood has high decay resistance; second-growth heartwood generally has only low to moderate resistance. (Wood Handbook, p. 2-17)
Strength: Old-growth redwood is moderately light, strong, stiff and hard. Douglas-fir varies widely in weight and strength, and the Handbook advises the denser wood where strength matters. (Wood Handbook, p. 2-11 to 2-17)
Uses: Redwood goes into siding, decking, outdoor furniture, tanks and fence material. Douglas-fir goes mostly into building lumber, beams, plywood and millwork. (Wood Handbook, p. 2-11 to 2-17)

For any other pair, open each species page from the wood hub; every page uses the same layout and the same sources.