What racket “density” should I use—and what do 3K–18K mean?

Core density (feel):

• Soft – most forgiving & arm-friendly; bigger sweet spot, longer dwell.
• Medium – best all-round balance for most club players.
• Hard – crisp/precise if you swing fast and hit clean.

Carbon weave (face stiffness):

• Fibreglass / 3K = softer, more comfort.
• 6K = a touch firmer.
• 12K = crisper, popular performance middle ground.
• 18K (and 24K) = stiffest, most direct power for advanced hitters.
  (Higher “K” ≈ stiffer face.)

Quick picks by level/style:

• Beginners / elbow care: Soft core + Fibreglass/3K.
• Most club players: Medium core + 3K/6K/12K.
• Attackers / advanced: Medium-Hard/Hard core + 12K/18K.

Brands you’ll see this on: Bullpadel (MultiEVA + 12K/18K), Babolat (X-EVA, Carbon Flex), Nox (HR3 in 3K/12K/18K), HEAD, Adidas, Wilson, Siux, Varlion, Royal Padel, Kuikma—and Skull Padel, which offers 3K through 18K (some 24K).