I tried it out on an old t-shirt. You need a long-sleeved one because the sleeves are used for the extra material. If you are good at mixing fabrics, textures etc you could use a different fabric - but I'm completely useless at that.
This one was done quite a while ago, so I only have after shots, but here is a pic of what you have to do.
- First you have to measure everything. Always measure and re-measure to be sure you have enough material.
- Decide where you want your sleeves to end (remembering to include room for the sleeve hem). Make sure that the cut-off part of the sleeve (the blue) when doubled (there are 2 sides to the sleeve) and joined together is enough to span the length of the complete side of the t-shirt from hem to sleeve (this is shown by the red line)
- Re-measure before cutting.
- You can include the hem of the original sleeve and sew to the hem at the bottom of the t-shirt.
Here are some after pics.
This is the side insert:
This is the front:
Et voila! Upsized and wearable!