This bobble cardigan is made from the top down, using a simple half double crochet (half treble crochet UK) stitch and bobble stitch.

Pictured with the baby and child skyler cardigan in my other listings.

Materials
Universal Yarn Cotton Supreme Waves, Shade 903 Gemstones, 100% Cotton dk / weight 3 yarn (210 metres / 230 yards per 100g)
3.5 and 4mm crochet hooks
See size chart sizes and yarn amounts

If you want to make with a thicker yarn like aran it could easily be adapted by making a size or 2 smaller than you want, using a size bigger hook.
The best way to find out what size to follow is:
Chain required stitches for your chest measurement and follow the size that has the nearest amount of stitches after divide for armholes, (size xs is 135 stitches after divide for armholes) and would turn out a size s with aran and a 5mm hook.

Written in English US terms with abbreviations for UK terms

Gauge
18 stitches x 8 rows of hdc and 3 rows of sc = 4” using a 4mm crochet hook

The PDF is 29 pages with photos.