- Reptation
- Research reactors
- Residence time
- Residual stress
- Resilience
- Resin
- Resistance thermometers
- Resistor
- Resonance
- Respiratory acidosis
- Respiratory system
- Respiratory tract
- Restoring force
- Resultant force
- Retaining walls
- Retarders
- Retina
- Retorts
- Reuptake
- Reversal potential
- Reverse osmosis
- Reversible process
- Reversible reaction
- Rhenium
- Rheology
- Rheometers
- Rheopecty
- Rheumatoid arthritis
- Rhodium
- Rhodochrosite
- Rhombus
- Rhyolite
- Rib cage
- Ribbon cables
- Rice hulls
- Ridges
- Riebeckite
- Right angles
- Right-hand rule
- Rigid body
- Rigidity theory
- Ring
- Risk factors
- River deltas
- River engineering
- Rivers
- Rivets
- Road
- Road junction
- Road rollers
- Road surface
- Roasting
- Robot welding
- Robotic materials
- Rock bolts
- Rock flour
- Rock fragment
- Rocket engine
- Rocket engine nozzle
- Rocket propellant
- Rockets
- Rocks
- Rockwell scale
- Roll forming
- Rolling
- Rolling-element bearing
- Roman aqueducts
- Roman cement
- Roman concrete
- Roof
- Roof shingles
- Roof tiles
- Room air distribution
- Room temperature
- Roots blowers
- Rotary hammer
- Rotary kilns
- Rotary vane pump
- Rotational energy
- Rotational symmetry
- Rotodynamic pump
- Rotor wing
- Rotorcraft
- Roughing pump
- Roving
- Rowing
- Rubber elasticity
- Rubberized asphalt
- Rubble
- Rubble masonry
- Rubidium
- Rubisco
- Ruby
- Rule of mixtures
- Rumble strips
- Runoff
- Runway
- Rupture disc
- Rut
- Ruthenium
- Rutherford backscattering spectrometry
- Rutile
- Rydberg constant
- S waves
- S-process
- S100 protein
- SANS
- SATA
- SCE
- SCSI
- SEC
- SIMS
- SMAW
- SMC
- SMR
- SOFC
- SOI
- SOS
- SSD
- SST
- STM
- Saccharin
- Sacrifice zones
- Sacrificial metal
- Safe-life design
- Safety barriers
- Safety engineering
- Safety glass
- Safety valve
- Safety-critical systems
- Sails
- Saint-Venant's principle
- Saline water
- Salinity
- Salt
- Salt lakes
- Salt mining
- Salt well
- Samarium
- Sand
- Sand casting
- Sand filter
- Sand mining
- Sandblasting
- Sandcrete
- Sandpaper
- Sandstone
- Sandwich panels
- Sandwich theory
- Sanidine