When choosing knit fabrics for tshirt construction, you have to consider how the fabric's properties, specifically its weight, thickness, drape, and stretch, will interact with the fit of your pattern. When Lycra® or elastane is blended into knit constructions, it fundamentally alters the fabric's core physical properties: stretch and recovery. This completely shifts how a pattern maker approaches draft ease for different silhouettes. So if you're were wanting a sleek fitted tshirt, choose a fabric with Lycra or elastane. If you prefer a boxy tshirt shape you would choose a standard single jersey or an interlock knit. Want a semi fitted tshirt - try a standard single jersey.