Plötulopi is an unspun Icelandic wool, also called pencil roving. It comes in nicely wound, flat rolls, called plates; in Danish, the yarn is also called "Pladegarn" ("plate yarn") - hence the pattern name.
The unspun quality of this yarn makes it more prone to breakage than other yarns. If the yarn breaks, you can just lay the two strands next to each other and knit with two strands for a couple of stitches.
This pattern is to make a thicker blanket working two strands together, which makes it possible to make an even more subtle gradient. The ends are taken from either side of the plate and one strand switched to a new color plate when you have approximately 25g of the first plate left.
The sample is made using 5 plates á ~100g of yarn, in adjacent colors. Instructions are given for making sure you make the most out of your yarn, using every single bit.
Instructions for both 1 strand and 2 strand versions are given, as well as instructions for how to size the blanket up