Léttlopi is a highly versatile yarn. It is equivalent in thickness to half a Álafosslopi. Léttlopi garments are lovely to wear both indoors and outdoors.

Material: 100% new wool
Ball: 50 g ~ approx 100 m
Suggested needle sizes: 4-5 mm
Gauge 10×10 cm: 18 stitches and 24 rows

Heavy Worsted weight (aran weight) yarn
100% new wool. 50 g (1.7 oz) approx. 100 m (109 yd).
Gauge: 18 sts to 10 cm (4”) over St st using size 4½ - 5 mm (Old UK 7-6) (US 7-8)

Care:
Hand Wash Cool
Do Not Iron
Do Not Dry Clean
Do Not Bleach
Do Not Tumble Dry
Dry Flat

Handwash only in lukewarm water (30°C or 86°F). Soak the garment in the suds for about 10 minutes, then rinse thoroughly in lukewarm water. Do not rub or wring but gently squeeze the liquid through the garment. If necessary, spin for about 1/2 minute to remove excess moisture. Dry flat, smoothing the garment out and pulling gently into shape.

https://istex.is/en/vorur/lettlopi/

It was also marketed in the US as Reynolds Lite-Lopi with a different color numbering system and label.