38B Sister Size Adjustments: When to Go Up or Down in Band

Understanding sister sizing for 38B opens up more options when a particular bra is out of stock or does not fit quite right. The direct sister sizes for 38B are 36C (sister down: tighter band, larger cup) and 40A (sister up: looser band, smaller cup). Each serves a different purpose depending on your needs.

Go with 36C when you want more support and the 38 band feels slightly loose even on the tightest hook. The 36 band will be firmer, providing better weight distribution, while the C cup maintains the same volume as the B. Use a band extender if the 36 feels too tight at first -- this gives you a middle ground between 36 and 38. Go with 40A only if you are between sizes or if the 38 band feels restrictive and you prioritize comfort over maximum support, keeping in mind that a looser band puts more strain on the straps.

As a rule of thumb, stick with the band size that matches your snug underbust measurement and use sister sizes only as a backup option for specific bras that run unusually tight or loose.