The following research materials are traditionally used for writing an essay:

Books: the notion of book needs no explanation. These are a solid background for a good essay since they provide you with a lot of information on certain research paper topic.

Journal articles: journal is a collection of academic writing pieces on different questions which often have scientific character and use scientific approach in observing issues. Journals are composed by a number of writers which contribute to different topics within one volume. Mainly it’s a periodical publication.

Databases: these are digital stores of information. Very often you need to have access to them which is granted via payment. It’s an effective source of research since it doesn’t involve paper or leg work.

Internet: this research tool has become very popular lately since it’s the easiest way to find the information. However it has some disadvantages: you can’t always trust the information you find, it’s sometimes very hard to find something on the topic, the articles are not always edited. Therefore it’s beneficial to use trustworthy services and web-sites.