Core species: ayous, kiri, balsa, limba, abachi

Section 8.1 explained that the core is the central ply of a blade, the one that absorbs energy and defines much of the feeling. In a symmetrical construction of five or seven plies, everything surrounding the core — intermediate plies, outers, composite where present — modifies its behaviour, but does not replace it. Choosing a core species is, in a sense, choosing the base character of the bat.

What is asked of a core wood is that it be light, that it absorb vibration well and that it offer a controlled elastic deformation. Dense, hard woods are no use here: they would transmit the impact too directly and add weight where it is least needed. The usual species therefore share a similar profile — soft, of uniform grain, with a good ratio of lightness to elasticity — though each contributes shades the player perceives.

Ayous (Triplochiton scleroxylon) is the most widespread core species in the industry. It comes from West Africa, is light, straight-fibred and of stable density between pieces. Its response is neutral: neither especially soft nor stiff, neither very absorbent nor very reactive. That neutrality is precisely its virtue. An ayous core imposes no character; it lets the outer plies and the rubber define the personality of the bat. It therefore appears in blades of every range, from beginner models to high-end attacking bats. If a spec sheet does not mention the core species, it is most likely ayous.

Kiri (Paulownia tomentosa) is the Japanese alternative to ayous, and the lightest of the usual species. Its density can fall below 250 kg/m³, against the 350-400 of ayous. That extreme lightness makes it possible to build fast blades with a very contained total weight, which has made it the preferred core of many Japanese attacking models. The trade-off is lower structural density: kiri absorbs less energy than ayous, which produces a drier, more direct touch. In five-ply blades that translates into a slightly shorter dwell time; in seven-ply ones the effect is damped by the additional plies.

Balsa (Ochroma pyramidale) is lighter still than kiri, with densities that can be around 120-180 kg/m³. Its use as a core has become popular over the last two decades, above all in designs seeking maximum speed with minimum weight. Balsa is extremely soft and its very porous cell structure makes it more absorbent than any other species on this list. In practice, a thick balsa core acts almost as a wooden sponge: it damps the impact noticeably and generates a mechanical catapult effect when combined with stiff outer plies. Some modern blades with a balsa core — such as the Butterfly Balsa Carbo X5, with two carbon plies — exploit this combination to achieve fast bats that retain a degree of absorption. The risk is that balsa, being so soft, contributes less lateral stability; it is therefore usually combined with hard intermediate plies or with composite, rather than used in pure all-wood constructions.

Limba (Terminalia superba) appears in the index as a core species, but its use in that position is less frequent than as an outer or intermediate ply — where it is dealt with in 9.3. Used as a core, it offers a middle point between ayous and the denser woods: somewhat firmer, with a less neutral response and a touch some manufacturers describe as “warm”. Its density, around 500-550 kg/m³, places it at the upper limit of what is considered a conventional core wood. In practice, a limba core stiffens the assembly and reduces the overall flexing, which brings the all-wood blade close to composite territory in stiffness without adding synthetic fibre.

Abachi (Triplochiton scleroxylon, another trade name for ayous) is sometimes listed as a distinct species, but botanically it is the same as ayous. The distinction is commercial, not technical: it is the same wood sold under different names depending on the market — “abachi” in Germany, for example, or “obeche” in Britain. In practice, a core labelled abachi behaves exactly like an ayous one.

What unites all these species is their function: to provide the elastic base on which the other plies work. The choice of core is not perceived in isolation — it is always filtered through the outer plies, the total thickness and the rubber — but it governs the floor on which everything else is built. The same five-ply design with koto outers can feel very different according to whether it carries a kiri or an ayous core, above all on slow and medium strokes where the deformation of the centre of the blade comes into play. The outer plies, which are the first to receive the impact and the ones that most govern the immediate response, are dealt with in the following section.