Make mesh watertight

With the t-shirt shape finalized, make your mesh watertight by "sealing" the holes at the neck, waist, and wrist. A watertight shape ensures that only the top visible surface of the mesh is exposed at any angle. If an asset is not watertight, it may expose backfaces (single-sided faces) that could affect the rendering of your asset and performance when equipped to a character.

<img src="https://prod.docsiteassets.roblox.com/assets/art/accessories/creating/Watertight-Top.png" />

Watertight top view

<img src="https://prod.docsiteassets.roblox.com/assets/art/accessories/creating/Watertight-Bottom.png" />

Watertight bottom view

To make your t-shirt watertight:

With LongSleeve active, switch to Edit mode.
Starting with any hole in the mesh, hold Alt and click the last edge on the mesh. The entire edge highlights.
Press E to extrude the mesh, then click after a small extrusion is added.
With the new edge still selected, right-click and select Merge Vertices > At Center from the contextual menu.
Press G to grab the new vertex and reposition it within your t-shirt mesh.
Repeat until all the interior-exposing holes of your mesh are closed.

Note

You've completed the modeling section of this tutorial. If desired, download a reference project of this stage and compare it against your work.

There are a lot of techniques to create clothing. Try experimenting with the following techniques, tools, and processes to create additional unique assets:

Making asymmetrical clothing.
Blender's cloth simulation and other sculpting tools.
Various community sewing and fabric techniques for creating clothing on Blender.