Navy is a deep, rich color, that looks best in 100% virgin wool fabric. It does well in thick weaves without excess sheen. Too much smoothness to a weave can create a glossy, slick appearance that looks unnatural to the eye.
Thick wool fabrics make excellent navy suits with a matte finish that shows the color off to its advantage.
A lighter wool can keep the garment comfortable in warmer weather and still lends the natural drape of wool, which keeps the fabric even and close to the wearer’s body.
Exotic blends to include cashmere and mohair are desireable if one seeks extra softness and perhaps a lighter weight with similiar properties to wool.
Small percentages of artificial fiber in the weave are acceptable (US law allows a 3% variance – so what is declared 100% wool may actually be 97%), and even desirable in small quantities for strength and stretch resistance.
More than trace however points to cost-saving rather than well-thought construction and fabrics with more than 30% synthetic fiber should be avoided if you can afford it. Too much synthetic fiber in the weave creates a flat, plastic-like sheen that makes a suit look cheap and will cut its life significantly.
Fit matters in every suit, and most of all in a dark suit. A dark suit emphasizes the shape and presence of the wearer more than a lighter color would.
Excess fabric can make a man look slumped and saggy, while fabric that clings or pinches too tightly makes him look awkwardly oversized and straining at the seams. A fit that stays close to the body without pinching while moving is ideal for a dark suit like navy blue.
I think，men buying off-the-rack should also pay attention to collar size, which tends to be unnecessarily loose on many mass-produced jackets and will most likely need to be adjusted.