Seat belt webbing
A load-bearing textile with a surface finish on it — which is why the softest cloth in the cupboard is the wrong one.
What not to do
Microfibre cloth is unsafe on Seat belt webbing
Unsafe
Do not do this. The risk is established, and it is described below.
MICROFIBRE IS FORBIDDEN HERE, WHICH IS UNUSUAL. The maker's bulletin is explicit: use a cotton rag, do NOT use microfibre, because it may scratch and damage the belt's surface treatment.
Evidence
Strongly supported
Sources
ServiceNews Article A24030A: Seat Belt Slow to Retract
American Honda Motor Co., Inc., published via NHTSA · Manufacturer documentation
Relied on for: That a cotton rag is used and microfibre must not be, because such rags may scratch and damage the surface treatment on the seat belts. (states this directly)
In detail
Woven polyester webbing, engineered to a specified strength and carrying a surface treatment that governs how it slides through its guides. Both of those change how it should be cleaned, and neither is obvious from looking at it. The finish is the reason for an unusually counter-intuitive prohibition. A manufacturer's service bulletin specifies a cotton rag and states plainly that microfibre must NOT be used, because it may scratch and damage the belt's surface treatment. Microfibre is the default cloth on glass, screens, stainless steel and painted surfaces; here it is the abrasive. The load-bearing half sets the second boundary. Webbing has a rated strength, and anything that attacks the fibre attacks that rating invisibly — the belt looks unchanged. So the cleaner is specified as a NEUTRAL detergent at 5% in lukewarm water, and no authoritative source clears a bleach, a solvent or a degreaser for it. Where a belt has been exposed to something unknown, the question belongs to the vehicle's service department. Drying is passive. Air, not heat, and not under tension.
Sources for this page
Sources
ServiceNews Article A24030A: Seat Belt Slow to Retract
American Honda Motor Co., Inc., published via NHTSA · Manufacturer documentation
Relied on for: That the specified cleaner is a neutral detergent, dishwashing liquid mixed at 5% with 95% lukewarm water, that a cotton rag is used, and that microfibre must not be used because such rags may scratch and damage the surface treatment on the seat belts. (states this directly)