The air temperature inside Irish caves is generally about 8-10°C. However, this air is very damp and can cause severe heat loss leading to hypothermia if warm clothing is not worn.
For your first few trips, old clothing may be adequate. This should include woolen socks, track suit leggings, a T-shirt and woolen jumpers (several thin ones are better than one thick one).
A waterproof jacket and leggings will help keep you warm and dry, while rubber (wellington) boots are essential to protect your legs and ankles.
Rubber gloves will help protect your hands both from the cold and wet and from infections which might enter scratches.
Regular cavers choose between a wet suit for very wet caves or a one piece fleece (fibre pile) undersuit combined with a one piece PVC/Nylon over suit.
It is very important to bring a complete change of clothes and towel to use after your caving trip.