Text in a flex container doesn't wrap in IE11

Add this to your code:

.child { width: 100%; }

We know that a block-level child is supposed to occupy the full width of the parent.

Chrome understands this.

IE11, for whatever reason, wants an explicit request.

Using flex-basis: 100% or flex: 1 also works.

.parent {
  display: flex;
  flex-direction: column;
  width: 400px;
  border: 1px solid red;
  align-items: center;
}
.child {
  border: 1px solid blue;
  width: calc(100% - 2px);       /* NEW; used calc to adjust for parent borders */
}

<div class="parent">
  <div class="child">
    Lorem Ipsum is simply dummy text of the printing and typesetting industry
  </div>
  <div class="child">
    Lorem Ipsum is simply dummy text of the printing and typesetting industry
  </div>
</div>

Note: Sometimes it will be necessary to sort through the various levels of the HTML structure to pinpoint which container gets the width: 100%. CSS wrap text not working in IE

I had the same issue and the point is that the element was not adapting its width to the container.

Instead of using width:100%, be consistent (don't mix the floating model and the flex model) and use flex by adding this:

.child { align-self: stretch; }

Or:

.parent { align-items: stretch; }

This worked for me.

As Tyler has suggested in one of the comments here, using

max-width: 100%;

on the child may work (worked for me). Using align-self: stretch only works if you aren't using align-items: center (which I did). width: 100% only works if you haven't multiple childs inside your flexbox which you want to show side by side.