Gloves, do they loose insulation ?

[flat-pack]

Have a pair of Lewiskit gloves, 2 part jobbies, inner is thin 'insulate' type and outer is waterproof. Bought last year and had no issues with cold digits.
But last night my fingers, especially thumbs, got soooo cold it was an effort to use the gear change.
So do they loose effectiveness ? should I wash them regular or what ?

Any rec's for toasty gloves appreciated

Graham