double strokeWidth

How wide to make edges drawn when style is set to PaintingStyle.stroke. The width is given in logical pixels measured in the direction orthogonal to the direction of the path.

Defaults to 0.0, which correspond to a hairline width.

Source 

double get strokeWidth {
  return _data.getFloat32(_kStrokeWidthOffset, _kFakeHostEndian);
}
void strokeWidth=(double value)

Source 

set strokeWidth(double value) {
  assert(value != null);
  final double encoded = value;
  _data.setFloat32(_kStrokeWidthOffset, encoded, _kFakeHostEndian);
}