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We study properties of twisted unions of metric spaces introduced by Johnson,Lindenstrauss, and Schechtman, and by Naor and Rabani. In particular, we provethat under certain natural mild assumptions twisted unions of $L_1$-embeddablemetric spaces also embed in $L_1$ with distortions bounded above by constantsthat do not depend on the metric spaces themselves, or on their size, but onlyon certain general parameters. This answers a question stated by Naor and byNaor and Rabani.  In the second part of the paper we give new simple examples of metric spacessuch their every embedding into $L_p$, $1\le p<\infty$, has distortion at least$3$, but which are a union of two subsets, each isometrically embeddable in$L_p$. This extends an analogous result of K.~Makarychev and Y.~Makarychev fromHilbert spaces to $L_p$-spaces, $1\le p<\infty$.

On $L_1$-embeddability of unions of $L_1$-embeddable metric spaces and of twisted unions of hypercubes