Simple Sass mixing to add shorthand (and specific) padding while converting units to 'rem' with the Bourbon function rem().

pad.scss

@mixin pad($paddings, $shorthand: true) {
  $orientations: top right bottom left;

  @if $shorthand {
    @each $value in $paddings {
      $paddings: set-nth($paddings, index($paddings, $value), rem($value));
    }
    padding: $paddings;
  } @else {
    @for $i from 1 through length($paddings) {
      @if nth($paddings, $i) != x {
        padding-#{nth($orientations, $i)}: rem(nth($paddings, $i));
      }
    }
  }
}