If the acrylic is crimped - run through heated rollers with a milled profile, you can get another 25 percent of thickness for the weight of fibre.

Although there is only a small percentage of acrylic in the mix it will affect the loftiness of the cloth, making it feel thicker than the equivalent weight, or lighter than the equivalent thickness of an all wool material.

Thats an interesting way to pleat, alternately to the stripe - presumably for frugality, but it makes a good effect.

Plus - you wear it well, Hamish - and the 'natural' white is far nicer than a 'pure' white which I think looks cheaper somehow, more man made.