GSM has become the way in which most users think of the thickness of the paper they are using and it is fair to say that a 100GSM paper will feel thicker than an 80GSM paper as it has 25% more weight to it. So this is actually a good way of weighing up (pun intended!) which paper you would use for a particular type of job.
Whilst there are no hard and fast rules as to what paper is used for which type of work there are some ways in which paper weights have become regarded almost as standard. 80GSM paper for example has become the workhorse of the paper world and is used possibly more than any other weight of paper, especially in business use, for things such as photocopying and general everyday tasks such as printing off an email. The reason 80GSM has become so ubiquitous is that it offers a very good balance between quality and price. Lighter paper would have cost benefits but would feel flimsier whilst heavier paper such as 100GSM would cost more and offer little benefit in everyday use. 100GSM paper is also thicker so could actually prove to be a disadvantage if documents are being printed out for archiving or storage purposes as they would require more storage space.
However for uses where a good impression counts 100GSM is a good choice and is generally the weight used for business stationery such as letterheads and compliment slips. The extra weight compared to 80GSM paper gives a more substantial feel and with the right design for the letterhead can have a high quality feel to it. Even the best design can lose its impact if the paper choice is wrong.
But although GSM is a fairly good way in which to select paper it is not the only factor to consider. Bulk is connected to the grammage but it concerns the density of the paper and is a different way to gauge the thickness of the paper. To understand how this works it would be useful to compare a sheet of 100GSM bond paper with a sheet of 100GSM art paper or coated paper. You will feel that the art paper has a thinner feel to it even though the GSM is the same. That is because the paper is denser. A paper with more density will have a smoother finish and will have less opacity which means that printing is less likely to show through from one side to the other.
Talking to your printer (in terms of our suggestion, that is always Circle Leaflet Printing) will help make the decision about which weight of paper to choose. They have knowledge about what is available and experience of what works in different circumstances. Ask for samples before you commit to a choice, printed samples may be better as you can see then how a finished job looks and feels on any particular weight.
It is possible to get a bit overwhelmed by all this stuff though and most people will simply choose a paper because they like it or because it works well as part of their corporate image. Put simply, if it looks right and feels right then it probably is right!