3g Opaque will image great and look nice
initially.
But 2 inescapable
facts.
1. If you machine wash and dry it will eventually crack. Not a question of if,
but when.
2. The first time your customer puts in in a hot dryer it will shrivel up like fried bacon, then it is FUBAR, GORY, and throw it away time.
Iron all for darks WILL NOT CRACK EVER nor shrivel up. Fact
When you wash test the min should be 25 wash/dry cycles in a real washing machine and dryer.
If you are OK with telling your customers that they should NEVER
machine wash and dry (hand wash and hang dry) then 3G Opaque is the paper for you.

Otherwise the tshirt will crack before 25 washes. Typically 10 -15.