This is a knit base with lots of stretch! This is TTS but if your kiddo is in between sizes, we recommend sizing down! -A Posh Piglet Exclusive Design! ***PLEASE NOTE: If any ready-to-ship items are included with this order, they will not ship until the preorder has arrived. In order to received any ready-to-ship items immediately, please place a separate order. Don't combine items from different PO's. Items will not ship separately, they will ship when the last preorder arrives! ***