They are not the same method, and the difference is water
The two terms get used interchangeably and they are not interchangeable. A dry method works essentially without water: light film and dust are lifted into the media and carried away. A rinse-less wash uses a solution of polymers and surfactants that encapsulate and lubricate the soil so it releases from the paint and stays suspended in the towel rather than being ground back into it. The solution is doing the job rinse water normally does. That single difference is what widens the band of soil a rinse-less wash can safely take on, and it is why standard airframe cleaning doctrine is blunt about the limits of a dry method: airport film, dust and light soil, and expressly not heavy carbon, grease or oil, engine exhaust areas above all.
The lubrication has to come out of the bottle
With no rinse carrying soil off the surface, the solution itself is the only thing between the contamination and the clearcoat. That puts the dilution ratio out of the crew's hands. It is the manufacturer's number, it is measured rather than judged by eye on a hot ramp, and a mix thinner than stated removes the lubrication while looking identical in the bucket. The product also has to be qualified for an airframe rather than a car. Cleaners specified to AMS 1526 are tested not to corrode aluminium, magnesium and steel alloys and not to adversely affect acrylic glazing, which matters when the same media passes over windows and unpainted skin in the same pass. The wider aerospace qualification standard for exterior cleaners and polishes, Boeing D6-17487, goes further again: sandwich corrosion over seven days of cyclic humidity and heat, acrylic crazing, paint softening, and hydrogen embrittlement to ASTM F519, four notched cadmium-plated specimens held under load for 150 hours. A consumer product cannot have passed a test it was never submitted to.
Where it goes wrong, and it is always technique
The failure cases belong to the operator, not the method. A thin mix is the single most common cause of marring. After that comes reusing loaded media, working a whole side with one towel, and letting the solution flash off in the Georgia sun before it is wiped. A rinse-less wash done with a single bucket, a thin mix and two towels will mar a clearcoat in one afternoon. That damage is not cosmetic bookkeeping. An aerospace clearcoat builds to roughly two to two and a half thousandths of an inch, correction spends film off that figure permanently, and nothing puts it back except a strip and repaint.
What a correct rinse-less wash looks like on the ramp
One panel at a time. Generous solution, not a mist. A fresh clean face of media for every pass, towels retired the moment they are loaded rather than folded once more, and a separate drying towel that never touches the ground. It is slower than most people expect and it consumes far more clean media than most people expect, and that consumption is the entire safety margin. There is no product that makes a rushed rinse-less wash safe. When the turn does not allow the time to do it that way, the honest answer is a dry wipe-down of the surfaces that show and the full wash at the next stop.
Neither method protects anything
Both are removal processes. Neither leaves anything behind that resists the next week of ramp film, brake dust and exhaust soot. How long the aircraft stays presentable is decided entirely by what is underneath the soil, which is a sealant, a ceramic coating, or bare clearcoat, and that is a separate decision with a separate scope. Anyone selling a wash as protection is describing something else. The useful question before booking either method is what is currently on the paint, because on bare clearcoat the film comes back at the same rate whichever way you washed it.
Two different jobs, not two grades of one
A dry wash is a defined, narrow piece of work: light film, the surfaces that show, one crew member, one pass, finished inside a turn. A rinse-less wash is a different job with a different scope. It covers the whole airframe panel by panel, it consumes clean media at a rate that surprises people the first time they watch it, and it carries soil a dry method would drag. Choosing the dry wash because it is the quicker job is sound. Choosing it for an airframe that needs the other job is not a saving of any kind, because the soil it cannot lift goes into the clearcoat instead, and clearcoat is the one thing on the aircraft that does not grow back.
What changes the answer
Three things, in order. The soil load: belly and exhaust areas carry hydraulic fluid, fuel and soot, and those accumulated soils hold corrosive material against structure, so they are not a rinse-less or a dry-wash problem at all, they are a degreasing job with its own products and its own time. The ramp: where wash water is restricted the reason is usually stormwater discharge, the rule varies field by field and hangar by hangar, and where no water may be used the decision has already been made for you. The clock: a departure in ninety minutes is an argument for a dry wipe-down of the leading edges, entry area and glass, not for a compromised full wash.