One of the most common faults on the old "rubber key" spectrums are groups of non working keys, or a completely non-working keyboard where it is impossible to get past the startup Sinclair copyright screen. This problem is almost always caused by a worn keyboard membrane.
These are brand new, high quality replacement membranes, manufactured in the UK in 2020 with high quality, more rigid, modern materials, but to the Samsung style specification of the original machines. This means they will have the same sensitivity and feel in use as the originals (which is most people's preference), but without the problems of sensitivity to heat and cracking over time.
Please note that this membrane IS NOT suitable for the 48K / 128K Spectrum+ machines - a larger membrane is required for those machines - see "Related Products" below.