So i have a “Hollow mesh” ( it has both an outer surface and an inner surface, This was due to the process used to make it ) that you can see here, Now, I want it to be filled essentially no surface inside because If i tried to rig it, It just goes weird, And i’d also like, if possible to not change the UV layout, Here’s the image of the shirt mesh
Welcome to BA 
Add a solidify modifier
Also welcome 
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…i have to contradict 
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select upper ngon, hide it, select the inner upper n-gon and a select more Ctrl- + until you reach what you wanna delete and delete… select the border and fill F…
But now you will also have plenty of space in the UVs
You may consider to not delete all of this but just some upper part and tighten this like so (?):
Ok thx but well it seemed that this does not seem to work with rigs It seemed to implode, Also note that the shirt, was built by using the model pre posed so I don’t really know if that has an effect, Here’s the vid
and the model https://drive.google.com/file/d/1KLwlD6_ENJOv0vNU3ElNeA9xSClidAE-/view?usp=share_link
First off all: you have a lot of single vertices… select one in edit mode and then select similar by amount of adjacent… and delete.
Second: the automatic weight is no magic button and do this on this object… if you have another object and do then the same the other object will properly will have another “weighting” which may not “match” … you might want to merge the body and the shirt to be one object or do another wighting … for example weight painting…
Or even look for some tutorials to get some experience into getting a usable weight of the mesh an armature…
