For a dorm room bed, do you just need the sheets to be XL twin or does your duvet/quilt/comforter etc. also need to be larger?
There is a five inch difference in length between a twin and twin XL bed – the difference is important primarily for the fitted sheet.
You definitely need Twin XL sheets as a regular Twin fitted sheet will not fit on a Twin XL bed. However, the comforter doesn’t NEED to be larger because it is not fitted but you’ll probably be happier if it is larger. I found it is easier to find Twin XL sheets than it is to find Twin XL comforters or duvets. My son bought a comforter that was NOT officially a Twin XL but it’s dimensions were 68" x 90" and it worked just fine.
Thanks!
Most comforters have 7 to 10 inches of overlap at the bottom so they drape over the foot of the bed. Dorm beds usually have a bar or something at the foot of the bed that would get in the way of an overlap so sticking with the regular sized comforter might work better (and save a few bucks and give you more options in color/style).
A full sized comforter would give you drape on the side which helps hide the stuff under your bed.
We bought a set with the XL twin sheets - I don’t know if the comforter is also proportionately longer, but I assume it is - and supplemented with an additional sheet set. Honestly, the sheets are the key here - a regular comforter would work fine.
We also got a full sized comforter to overhang the bed and hide what’s stored under the bed .
If the student is male, the chances the bed will ever be made is so small that the size of the comforter is irrelevant. 
check with the school housing website first! Some of the dorms at my sons schools have XL and others are just regular…don’t buy until you know for sure!
I was fine with twin sheets, but they were a stretchy material. Twin XL fits better. I don’t remember finding many twin XL comforters so I used a regular one with no issues. I didn’t use the comforter until I moved into an apartment since the dorm rooms were too warm all year. But other dorms were cold, so bring it in case. Many people also bought a mattress pad/mattress topper to make the bed softer.
Thanks. I was just talking to my mom about it and she seems to think I should get a twin XL comforter, but I’m not sure that such a thing even exists.