Underwear is a construction category
Briefs, bras, sports underwear and shapewear can use very different fibers and elastic components. A single hot-water rule would be unsafe for some of them. Read each label and separate delicate or heat-sensitive pieces before washing.
Cool or warm water covers many everyday loads
Cool water is a conservative option for lightly soiled items and delicate stretch fabrics. Warm water can be appropriate for many durable washable pieces when the label allows it. Heavy soil should first trigger sorting and compatible pretreatment rather than an automatic jump to high heat.
Protect elastic and structured pieces
Bras, lace and molded or bonded components often need gentler handling. A mesh bag may reduce snagging for machine-washable items, but it does not make a hand-wash-only garment safe for the washer.
Use the item-specific limit
The Wash Temperature Finder accepts a care-label maximum and caps the general starting point to that value. For bras, also review the dedicated item-care page before choosing the cycle and drying method.
Garment care labels, appliance manuals and laundry-product directions can be more specific than a general guide. Use them when they set a tighter limit.