What is the difference between Cat5e, Cat6 and Cat6a cable?
Successive specifications for twisted-pair Ethernet cable, differing in how well they resist interference — which is what determines the speed and distance they can support.
What all of them share. Four twisted pairs of copper, an RJ45 connector, and a 100-metre maximum channel length for Ethernet. The twisting is the essential engineering: twisting a pair causes interference to affect both conductors equally so it cancels out, and tighter twisting resists more interference.
Cat5e. Supports 1 Gbps reliably to 100 metres. Enhanced over the original Cat5 with tighter specifications on crosstalk — interference between pairs inside the same cable. Perfectly adequate for gigabit networking, which covers the overwhelming majority of home and small office use.
Cat6. Tighter twisting, higher tested frequency, and frequently a plastic spline separating the pairs. Supports 1 Gbps comfortably and 10 Gbps up to around 55 metres, depending on conditions and interference.
Cat6a. "Augmented" — supports 10 Gbps to the full 100 metres. Achieves this by controlling alien crosstalk, interference between adjacent cables in a bundle, usually through extra shielding or a thicker jacket. Noticeably thicker, stiffer and harder to route and terminate.
Cat7 and Cat8 exist, are shielded, and are largely irrelevant for ordinary installations — Cat7 was never recognised as an Ethernet standard by the relevant bodies in the way the others were, and Cat8 is a short-distance data centre specification.
What actually matters in practice:
Your equipment is almost certainly the limit, not the cable. If your switch, router and devices are gigabit, Cat5e is not holding you back and replacing it changes nothing.
Termination quality matters more than category. Untwisting too much of a pair at the connector, or a poor punch-down, degrades performance more than a lower category would.
Solid core for permanent runs, stranded for patch leads — solid conductors do not tolerate repeated flexing.
Shielded cable requires proper earthing, and badly earthed shielding is worse than none.
For new permanent installation, Cat6 or Cat6a is sensible, because the cable outlives several generations of equipment and re-cabling a wall is the expensive part.