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A known disposable razor company is claiming on their web site that their current product is superior to their old one because it has 5 blades instead of three.

You can see the claim on the "science" page here, watching the "Why Fusion is better than MACH3" videoclip.

Do five blades provide any proven advantage in comparison to three blades? For example, less cutting, or a deeper shave? The company only claims it's better, however I don't trust them, as they show only pseudo-scientific crap instead of real facts on their site.

Does any science back their claims?

See also The Economist:

enter image description here

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    While the question is great (+1), I must say that "known disposable razor company" wording is extremely amusing, seeing how you use their brand name 1 line below making the identification 100% unambiguous :) – user5341 Dec 14 '11 at 15:38
  • @DVK I didn't have any choice :-) – Sklivvz♦ Dec 14 '11 at 16:23
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    "Hyperbolic curve" seems appropriate, somehow. – Joel Rein Dec 15 '11 at 9:37
  • Anecdotally - I believe the fusion works much better for me after the first shave. If I dispose of the blade after a single use I do not notice much of a difference. But the Fusion seems to have a shave similar to the first shave for 3-5 shaves. Disposables tend to nick/not shave as close after the first shave and are basically unusable after a second for me. The fusion tends to feel smoother after a single pass the dispsoable twin blade takes 2-3 passes to get it to where I feel it is acceptable. – Chad Dec 15 '11 at 16:15
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    A tangential comment. While I have no idea whether a greater number of blades is better, I do know that the 5 bladed razor was predicted by the Onion: theonion.com/articles/… – George Lowther Dec 15 '11 at 22:39
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Studies that have ever been published or scrutinised outside razor companies seem to be rather difficult to come by.

The best I could find was Measurement of beard hair removal efficacy using image analysis, a study conducted by researchers at Gillette (kudos to Solveig_A on Reddit for fetching the full-text for me). Now, a warning: this study's primary focus was not actually about comparing two razors, but on techniques for finding statistically significant results even for marginal effects were to conduct such a study. That can make reading it a bit obtuse (I shall not get into why they might be motivated to conduct such a study...).

The first two experiments compare different types of shaving foam using a twin blade and a single-blade razor, respectively. They do not include results in such a way as to make direct comparison possible. However, the third experiment compared a single-blade and a twin-blade razor (Gillette's Trac I and Trac II razors, respectively) with the same type of shaving foam. According to their data, the twin-bladed razor was 1.6% more effective than the single-bladed razor, but that they could not reject the null hypothesis (that they were equally effective) at the α=0.05 significance level.

In short, this does not represent compelling evidence that a razor with two blades is more effective than a razor with one blade, which does not bode well for the claim that five blades are more effective than three.

Cecil Adams, writing for The Straight Dope, cites studies by Consumers' Research magazine which consistently failed to find a benefit for twin blades, whilst noting that the single-bladed razors tended to last for more shaves than twin-bladed razors.

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It is difficult to say for certain without their scientific thesis to study over.

With that said there is some validity to wanting more razors, and some there are reasons against it.

Consider this Shaving technology

This in no way proves that adding more razors is purely for marketing purposes, but it helps raise the question understand that there is a point when there is too many razors and offers an idea to why there one is seeing more razors.

How stuff works

This describes that there is not a lot of information to go on, as this is a topic that scientists outside of Gillette rarely cover.

In addition only a minimum of two blades are required to cut and overcome nicking of the skin. The reason for adding more blades only further reduces that chance of nicking by not allowing the skin to 'hill'.

Apart from that it comes down to sampleing frequency. With two blades you can get a single cut from one stroke. One blunt blade to bunch the hairs, and second blade to cut them. With 4 blades you can cut twice with one stoke.

The final point to be made is that all designs have an optimal setting and razors are no different.

In a set distance we can place one razor.

              [--------------------------] no razor

              [------------/-------------] 1 razor

Certain qualities may be improved with two blades, such as reducing of nicks.

              [------/-----------/-------] 2 razors

Again we can increase the # of razors and some key parameters will improve, such as sample rate.

              [---/----/------/-----/----] 4 razors

When we reach the maximum possible number of razors. When the blades are paper thin, and there is no space left...

              [//////////////////////////] Theoretical infinite razors.

The razor can not cut any more, it has become useless and the key parameters have decreased to zero.

There does exists a key point in the middle where blade spacing and size give the highest performance. Optimization

*Note this curve is over simplified.

So what the Gillette company is claiming is not entirely false. However, again without there thesis it is hard to reproduce their results and validate their experimental claims. It might happen to be that any razors past 3 do nothing to increase the performance.

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    This seems like guessing/speculating as to why Gilette might be right. You postulated improving "stability" from 1->2 blades, but that was about it. Sorry, but your answer thus far is a narrative of your thoughts. Can you try to improve it with data/facts/sources? – Hendy Dec 13 '11 at 21:13
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    My attempt was to specify that is difficult to say if they are right or not but there is theory behind an optimal point. I can attempt to find out which key parameter Gillette looks for in their designs. I'm not certain if they release any of their experimental work though. – CMacDady Dec 13 '11 at 21:18
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    I think it's unsatisfactory, sorry: let's say Gillette came out with 8 blades. You answer could be used to justify a claim that 8 is better than 5. Let's say that Gillette stopped producing 5 blades and started producing 4 blades. Again, one could use your answer to justify that 4 blades are better. Your answer, basically, does not use the specific number of blades, and thus it does not, all in all, answer the question. – Sklivvz♦ Dec 13 '11 at 22:42
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    But there still exists science in Gillette's claim that more blades are better, your original question. They were vague allowing any number of things to be better. The fact that more blades increase sampling rate is 'better'. – CMacDady Dec 13 '11 at 23:30
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    As someone that shaves with single blade razors: blades don't "bunch" the hair, no matter how many there are; more blades in the same space increases the chance of getting clogged with hair; finer blades are generally more brittle and/or dull more easily. These manufacturers often cite "saved time" as a benefit for multi-blade razors in not having to go over the same area more than once. I find that no razor gives a clean shave in one stroke, and therefore most of what they are claiming is just marketing. You need to cite some real studies in this answer. – jozzas Dec 13 '11 at 23:47

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