I was browsing the internet looking for alternate proofs to why the electric field produced by an infinite sheet was equal to the charge density divided by twice the space permitivity constant. However, in my search I came across a proof that confused me at this link, http://www.physlink.com/Education/AskExperts/ae544.cfm It found the electric field produced to be eqaul to the charge density divided by only the space permitivity constant. My question is, what happened to the factor of 2. Are they only considering one face of the sheet but even then should that not decrease it by another factor of 2. What is going on here?