Purchased 14.99 including shipping (2 euros!) To:

http://www.audilo.com/
http://www.audilo.com/ER20-Bouchons-de-Musicien-Haute-Fidelite-pr-16138.html
This is the cheapest and most you can pay in any way (I even paid by check in a letter)

CAUTION: As mentioned on the website:
<p class="bbcode-cite"> Quote: <span>Etymotic ER20 Our caps are the original plugs! Other retailers sell these caps under other brands such as S-20 Pianissimo, Elacin ER 20 S or Audi Music ® ER-20S, often much more expensive. Do not be fooled, it is a question exactly the same product!</span>
So not only you pay less and in addition it is the original!
Patents are Etymotic, recognized brand that uses this system on a floor monitor.

Otherwise, there is indeed a world of difference between the foam and these plugs.
Means less strong without much altering the frequencies.
The only ones who do best are molded and cost hundreds of dollars ...
So do not hesitate!
Plan and also foam in addition, if the sound will be way too strong.

I almost became deaf in one ear after a Korn concert in Toulon with the most rotten that I heard in my life, without caps, of course, so do not play with it ... after it is too late ...
For those who are exposed every day and long (Inge live ...), only the cast will do.

Tip: to return, provide a small amount of lubricant (saliva, it works a lot) (I know is insidious: D)
Because he is really the return to be effective ...