Wingspan 11 to 13 mm. Another brown, rather nondescript species, which is most easily identified as an adult by reference to the genitalic structure as it is quite similar to some other Coleophora species.

The cased larva feed on oak.  The young overwintered larva are tiny but may be found on oak buds.  It has an oval leaf-fragment incorporated into the case, unlike similar species.  Eventually this is obscured.  Circular mines are made by the cased larva, each with a hole in the middle where the case was attached

Coleophora lutipennella has very similar cased larvae feeding on oak, lacking the oval leaf fragment 

Adult young cased larva

larval stage: only the young overwintered mines in Spring can be recorded; photograph the case showing the leaf fragment incorporated into the structure

Areas where the larval foodplant is present.

Adults appear in July and August and are attracted to light.

The larva produces a distinctive feeding pattern, creating small holes in the leaves of the foodplant, Evergreen Oak. A case is then created which is replaced as the larva grows.

In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as common.

Ocasional in Leicestershire and Rutland.

http://www.leafmines.co.uk/html/Lepidoptera/C.flavipennella.htm

https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/lepidoptera/ditrysia/gelechioidea/coleophoridae/coleophora/coleophora-flavipennella/