The shape I think of as a classic triangle shawl has a deep center point and two wide, symmetrical sides. This triangle shape is probably best for actually keeping your back and shoulders warm.
The very basic hap triangle without any lace detail or trim is a perfect shawl for a beginner knitter. It looks great in garter stitch, and although it can be plain, some self-striping yarn can jazz it up if you’d like. This shawl construction is easily spotted thanks to the center triangle of garter stitch with no visible increase line.
This shawl shape has a bottom point that doesn’t go too far down the back. These shawls can also be wrapped around the neck and tied off like a scarf or neckerchief. When knitted in a lighter yarn with a lace pattern, they make a pretty small shawlette that’s great for layering on brisk days that aren’t terribly cold.
The asymmetric triangle shawl is one of my all-time favorite shawl knitting patterns. This type of triangular shawl pattern only increases by one stitch every other row. This means it has one edge that stays vertical while the other side grows outward at an angle. This gives you a beautiful long edge to drape around your shoulders and thus creates a very wearable shape.
Shawl sizes are easily adjustable by changing yarn weights and your needle size. You can take a pattern for a triangle shawl written in worsted weight on US 8 (4 mm) needles, take it down to lace-weight yarn on US 1.5 (2.5 mm) needles, and turn it into a triangle scarf without making any other changes to the pattern.